Method and apparatus for beam selection in mobile communication system

ABSTRACT

The present disclosure relates to a communication technique for converging an IoT technology with a 5G communication system for supporting a higher data transmission rate beyond a 4G system, and a system therefor. The present disclosure may be applied to an intelligent service (e.g., a smart home, a smart building, a smart city, a smart car or connected car, healthcare, digital education, retail business, a security and safety related service, or the like) on the basis of a 5G communication technology and an IoT related technology. Disclosed are a method and an apparatus for reselecting a beam and selecting a suitable beam to be camped on, by a terminal, in order to be provided with a service in a next generation mobile communication system operating on the basis of a beam. Disclosed according to an embodiment of the present invention are a method and an apparatus for performing the same, the method comprising the steps of: receiving system information including first beam selection priority information; receiving a radio resource control (RRC) message including second beam reselection priority information; identifying whether the terminal has camped on a suitable beam; and applying one of the first beam reselection priority information and second beam reselection priority information on the basis of the result of the identification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage of International ApplicationNo. PCT/KR2017/008411, filed on Aug. 3, 2017, which claims priority toKorean Patent Application No. 10-2016-0100054, filed on Aug. 5, 2016,and Korean Patent Application No. 10-2016-0102609, filed on Aug. 11,2016, the disclosures of which are herein incorporated by reference intheir entirety.

BACKGROUND 1. Field

The present disclosure relates to a method and apparatus used when auser equipment (UE) reselects a beam to receive service and selects asuitable beam to camp on in a next-generation mobile communicationsystem that operates on the basis of a beam.

2. Description of Related Art

In order to meet wireless data traffic demands, which have increasedsince the commercialization of the 4G communication system, efforts todevelop an improved 5G communication system or a pre-5G communicationsystem have been made. For this reason, the 5G communication system orthe pre-5G communication system is called a beyond-4G-networkcommunication system or a post-LTE system. In order to achieve a highdata transmission rate, implementation of the 5G communication system ina mmWave band (e.g., 60 GHz band) is being considered. In the 5Gcommunication system, technologies such as beamforming, massive MIMO,Full-Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, andlarge-scale antenna technologies are being discussed so as to mitigatethe path loss of a radio wave in the mmWave band and increase the traveldistance of a radio wave. Further, the 5G communication system hasdeveloped technologies such as an evolved small cell, an advanced smallcell, a cloud radio access network (cloud RAN), an ultra-dense network,device-to-device communication (D2D), a wireless backhaul, a movingnetwork, cooperative communication, coordinated multi-points (CoMP),received interference cancellation, and the like, so as to improve thesystem network. In addition, the 5G system has developed advanced codingmodulation (ACM) schemes such as hybrid FSK and QAM modulation (FQAM)and sliding window superposition coding (SWSC), as well as advancedaccess technologies such as filter bank multi carrier (FBMC),non-orthogonal multiple access (NOMA), sparse code multiple access(SCMA), and the like.

Meanwhile, the Internet has evolved from a human-oriented connectionnetwork, in which humans generate and consume information, to theInternet of Things (IoT), in which distributed components such asobjects exchange and process information. Internet-of-Everything (IoE),in which big-data processing technology is combined with IoT via aconnection with a cloud server or the like, has emerged. In order toimplement IoT, technical factors such as a sensing technique,wired/wireless communication and network infrastructure,service-interface technology, and security technology are required, andresearch on technologies such as a sensor network, machine-to-machine(M2M) communication, machine-type communication (MTC), and the like forconnection between objects has recently been conducted. In an IoTenvironment, by collecting and analyzing data generated in connectedobjects, an intelligent internet technology (IT) service to create newvalue in people's lives may be provided. The IoT may be applied tofields such as a smart home, a smart building, a smart city, a smart caror connected car, a smart grid, health care, a smart home appliance, ora high-tech medical service via the convergence of conventionalinformation technology (IT) and various industries.

Accordingly, various attempts to apply the 5G communication system tothe IoT network have been made. For example, 5G communication technologysuch as a sensor network, machine-to-machine (M2M) communication,machine-type communication (MTC), and the like are implemented viaschemes such as beamforming, MIMO, array antenna, and the like. Theapplication of the cloud RAN as big-data processing technology may be anexample of convergence of the 5G technology and the IoT technology.

In a next-generation mobile communication system, a plurality of beamsmay be used. Also, a user equipment (UE) is capable of forming a beam byusing a plurality of beams or adjusting a beam width. In this instance,the UE may need to select a suitable beam to camp on from among aplurality of beams in order to receive a service.

SUMMARY

Therefore, the present disclosure has been made in view of theabove-mentioned problems, and an aspect of the present disclosure is toprovide a method of selecting a suitable beam to be camped on from amonga plurality of beams by taking into consideration the beamformingcapability of a user equipment (UE) in a next-generation mobilecommunication system.

Also, another aspect of the present disclosure is to provide a method ofselecting a beam configuration differently depending on whether a UE isin an idle state or is in a connected state in a next-generation mobilecommunication system.

Also, another aspect of the present disclosure is to define a procedureof efficiently reselecting neighboring beams by taking intoconsideration the difference in complexity that occurs when a UEperforms intra-transmission-reception-point (TRP) or inter-TRP beamreselection on the basis of the types of neighboring cells andmeasurement values in a next-generation mobile communication system.

In accordance with an aspect of the present disclosure, a method ofselecting a beam by a user equipment (UE) includes: receiving systeminformation including first beam reselection priority information;receiving a radio resource control (RRC) message including second beamreselection priority information; identifying whether the UE camps on asuitable beam; and applying one of the first beam reselection priorityinformation and the second beam reselection priority information basedon the result of the identification.

In accordance with an aspect of the present disclosure, a UE includes: atransceiver configured to transmit and receive a signal; and acontroller configured to receive system information including first beamreselection priority information, receive a radio resource control (RRC)message including second beam reselection priority information, identifywhether the UE camps on a suitable beam, and apply one of the first beamreselection priority information and the second beam reselectionpriority information based on the result of the identification.

According to an embodiment of the present disclosure, a suitable beamselection procedure is proposed in which a user equipment (UE) can takeinto consideration the beamforming capability of the UE in anext-generation mobile communication system that uses a plurality ofbeams, whereby the UE can efficiently select a suitable beam to camp on,and UE's idle operation may be implemented.

Also, according to another embodiment of the present disclosure, when areception beam is measured in a next-generation mobile communicationsystem, different configurations are applied to an idle-state UE and aconnected-state UE, thereby overcoming the case in which the amount oftime spent is different depending on the unique performance of a UE orthe case in which consistent performance cannot be secured.

Also, according to another embodiment of the present disclosure, gradedneighboring beam reselection criteria of the present disclosure areapplied to a next-generation mobile communication system that operateson the basis of a beam, whereby the number of times that inter-TRP beamreselection, which entails great expense for beam selection, isperformed is lower than the number of times that intra-TRP reselectionis performed, and additional operations of the UE may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure;

FIG. 1B is a diagram illustrating beam sweeping of a next-generationmobile communication system according to an embodiment of the presentdisclosure;

FIG. 1C is a diagram illustrating the structure of a subframe of anext-generation mobile communication system according to an embodimentof the present disclosure;

FIG. 1D is a diagram illustrating a process in which frequency-basedpriority information for cell reselection is broadcasted via an SIB oris applied to a preconfigured user equipment (UE) via an RRC connectionrelease message, which is dedicated RRC signaling, in a next-generationmobile communication system that uses a single beam according to anembodiment of the present disclosure, and is a diagram illustrating amethod of detecting a suitable cell;

FIG. 1E is a diagram illustrating a process in which frequency-basedpriority information for cell or beam reselection is broadcasted via anSIB or is applied to a preconfigured UE via an RRC connection releasemessage, which is dedicated RRC signaling, in a next-generation mobilecommunication system that uses a plurality of beams according to anembodiment of the present disclosure, and is a diagram illustrating amethod of detecting a suitable beam from among a plurality of beams;

FIG. 1F is a diagram illustrating a procedure of reselecting a suitablebeam in a next-generation mobile communication system that uses aplurality of beams according to an embodiment of the present disclosure;

FIG. 1G is a block diagram of the internal structure of a UE accordingto an embodiment of the present disclosure;

FIG. 1H is a block diagram of the configuration of a base stationtransceiver apparatus according to an embodiment of the presentdisclosure;

FIG. 2A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure;

FIG. 2B is a diagram illustrating beam sweeping of an NR systemaccording to an embodiment of the present disclosure;

FIG. 2C is a diagram illustrating the structure of a subframe of an NRsystem according to an embodiment of the present disclosure;

FIG. 2D is a diagram illustrating the overall operation according to anembodiment of the present disclosure;

FIG. 2E is a diagram illustrating the reception beam configuration of aUE according to an embodiment of the present disclosure;

FIG. 2F is a diagram illustrating operations of a UE according to anembodiment of the present disclosure;

FIG. 2G is a block diagram of the internal structure of a UE accordingto an embodiment of the present disclosure;

FIG. 2H is a block diagram of the configuration of a base stationtransceiver apparatus according to an embodiment of the presentdisclosure;

FIG. 3A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure;

FIG. 3B is a diagram illustrating the structure of a frame used by an NRsystem that operates on the basis of a beam according to an embodimentof the present disclosure;

FIG. 3C is a diagram illustrating a procedure in which a UE reselects acell in an LTE system;

FIG. 3D is a diagram illustrating a method in which a UE reselects aserving beam in an NR system according to an embodiment of the presentdisclosure;

FIG. 3E is a diagram illustrating a beam reselection method of an NRsystem according to an embodiment of the present disclosure;

FIG. 3F is a diagram illustrating operations of a UE when the UEreselects a serving beam in an NR system according to an embodiment ofthe present disclosure;

FIG. 3G is a block diagram of a UE according to an embodiment of thepresent disclosure;

FIG. 3H is a block diagram of a TRP in a wireless communication systemaccording to an embodiment of the present disclosure;

FIG. 4A is a diagram illustrating a procedure in which a UE and a basestation perform HARQ new transmission and retransmission in associationwith conditional transmission according to an embodiment of the presentdisclosure;

FIG. 4B is a diagram illustrating an operation by which a UE performsHARQ new transmission and retransmission in association with conditionaltransmission according to an embodiment of the present disclosure;

FIG. 4C is a diagram illustrating another operation by which a UEperforms HARQ new transmission and retransmission in association withconditional transmission according to an embodiment of the presentdisclosure;

FIG. 4D is a block diagram of a UE according to an embodiment of thepresent disclosure; and

FIG. 4E is a block diagram of a base station in a wireless communicationsystem according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail in conjunction with the accompanying drawings. In the followingdescription of the present disclosure, a detailed description of knownfunctions or configurations incorporated herein will be omitted when itmay make the subject matter of the present disclosure rather unclear.The terms which will be described below are terms defined inconsideration of the functions in the present disclosure, and may bedifferent according to users, intentions of the users, or customs.Therefore, the definitions of the terms should be made based on thecontents throughout the specification.

The advantages and features of the present disclosure and ways toachieve them will be apparent by making reference to embodiments asdescribed below in detail in conjunction with the accompanying drawings.However, the present disclosure is not limited to the embodiments setforth below, but may be implemented in various different forms. Thefollowing embodiments are provided only to completely disclose thepresent disclosure and inform those skilled in the art of the scope ofthe present disclosure, and the present disclosure is defined only bythe scope of the appended claims. Throughout the specification, the sameor like reference numerals designate the same or like elements.

In the descriptions below, terms used for identifying access nodes, theterms indicating network entities, terms indicating messages, termsindicating interfaces between network entities, terms indicating variousidentification information, and the like are used for ease ofdescription. Therefore, the present disclosure is not limited by theterms provided below, and other terms that indicate subjects havingequivalent technical meanings may be used.

For convenience of description, the present disclosure may use terms andnames defined in the 3rd-generation partnership project long-termevolution (3GPP LTE) standard, or terms and names that are modificationsthereof. However, the present disclosure is not limited to the terms andthe names, and may be equally applied to systems that comply with otherstandards.

First Embodiment

The first embodiment of the present disclosure relates to a method andapparatus used when a user equipment (UE) equipped with anext-generation mobile communication system (new radio (NR) or 5G) andLTE selects a suitable beam for wireless mobile communication. Theoperations of the UE in the embodiment of the present disclosure mayinclude the following steps.

A method and apparatus used when a UE selects a beam to camp on in thenext-generation mobile communication system.

-   -   A step in which an idle-state UE receives a downlink reference        signal by applying a first downlink reception beam        configuration. The downlink reference signal is transmitted in        an overhead subframe (osf), and at least one beam's downlink        reference signal may be sequentially transmitted in a single        osf.    -   A step for determining whether the downlink reference signal        satisfies a first condition    -   A step for regarding the corresponding beam as a suitable beam        when the downlink reference signal satisfies the first condition    -   A step of camping on one of the suitable beams

The first condition is satisfied when a first calculation value isgreater than or equal to 0. The first calculation value is determinedusing an equation which takes a downlink reference signal strength andan uplink compensation factor as inputs. The uplink compensation factoris determined using an equation that takes the uplink transmission beamconfiguration capability of a UE and the power class of the UE asinputs. The uplink transmission beam configuration capability of the UEmay be defined for each band of the next-generation mobile communicationsystem supported by the UE. Also, in the first downlink reception beamconfiguration, the number of downlink reception beams (a reception beamwidth or a sweeping length) may be determined by a combination of afirst parameter and a second parameter (or the lower of the two values).The first parameter is information related to the number of receptionbeams supported by a UE, and the second parameter is a preconfiguredinteger set in advance for each frequency band.

In the descriptions below, terms used for identifying access nodes, theterms indicating network entities, terms indicating messages, termsindicating interfaces between network entities, terms indicating variouspieces of identification information, and the like are used for ease ofdescription. Therefore, the present disclosure is not limited by theterms provided below, and other terms that indicate subjects havingequivalent technical meanings may be used.

For convenience of description, the present disclosure uses terms andnames defined in the 3GPP LTE (3rd-generation partnership projectlong-term evolution) standard. However, the present disclosure is notlimited to the terms and names, and may be equally applied to systemsthat comply with other standards.

FIG. 1A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1A, a radio access network of the next-generationmobile communication system includes a next-generation node B (a newradio node B, hereinafter referred to as an NR NB or a base station) 1a-10 and a new radio core network (NR CN) 1 a-05, as illustrated in thedrawing. A user equipment (a new radio user equipment (NR UE) or UE) 1a-15 may access an external network via the NR NB 1 a-10 and the NR CN 1a-05.

In FIG. 1A, the NR NB 1 a-10 may correspond to an evolved node B (eNB)in a legacy LTE system. The NR NB is connected to the NR UE a1-15 via aradio channel, and may provide better service than a legacy node B. Inthe next-generation mobile communication system, all user traffic isserviced via a shared channel, and thus a device that collects stateinformation of UEs, such as a buffer status, an available transmissionpower status, a channel status or the like, and performs scheduling isneeded, and the NR NB a1-10 takes charge of the same. One NR NBgenerally controls a plurality of cells. In order to implementhigh-speed data transmission when compared to the legacy LTE, abandwidth greater than or equal to the maximum legacy bandwidth may beneeded, and orthogonal frequency division multiplexing (OFDM) is used asa radio access technology, and beamforming technology is additionallyused. Further, an adaptive modulation and coding (hereinafter, referredto as AMC) scheme, which determines a channel coding rate and amodulation scheme on the basis of the channel status of the UE, isapplied to the LTE system. The NR CN 1 a-05 supports mobility,configures a bearer, or configures quality of service (QoS). The NR CNis a device that is in charge of various control functions in additionto a mobility management function associated with a UE, and may beconnected to a plurality of node Bs. Also, the next-generation mobilecommunication system may interoperate with the legacy LTE system, andthe NR CN may be connected to an MME a1-25 via a network interface. TheMME is connected to an eNB a1-30, which is a legacy node B.

The NR is aimed at supporting a more improved data transmission speedthan the legacy LTE. As a method of increasing a data transmission speedin the NR, a method is considered in which a signal is transmitted usinga wide frequency band existing in a frequency band greater than or equalto 6 GHz. That is, it is considered to use a millimeter wave(hereinafter mmWave) band, such as a 28 GHz band, a 60 GHz band, or thelike, in order to increase a transmission rate. In a frequency band,which is considered for mmWave, signal attenuation per distance isrelatively large, and thus transmission on the basis of a directionalbeam generated using multiple antennas is required in order to securecoverage. In the case of the directional-beam-based transmission,transmission or reception of a signal may be difficult at a locationwhere a beam is not formed. In order to overcome the above-describeddrawback, beam sweeping is used. Beam sweeping is a scheme in which atransmission apparatus sequentially sweeps or rotates and transmits adirectional beam having a preconfigured beam width, such that a beam isreceived by a reception apparatus that exists within the beam range ofthe transmission apparatus.

FIG. 1B is a diagram illustrating beam sweeping of a next-generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1B, for example, a transmission reception point (TRP)1 b-05 (a device for transmitting and receiving a radio signal in anetwork, a 5G NB, or a device connected to a 5G NB) transmits adirectional beam having a preconfigured width at a preconfigured pointin time t1 in a preconfigured direction, and transmits a directionalbeam having the same width at t2 in another direction, or the like,whereby the beams are transmitted in all directions during apreconfigured period of time. Accordingly, a downlink signal transmittedby a base station arrives at a UE 1 b-15 at t9, and arrives at a UE 1b-10 at t4.

Beam sweeping is mainly used when a base station does not know theorientation of a directional beam to be applied to a UE, and a commonoverhead signal to be transmitted to an idle-state UE may be transmittedvia the beam sweeping.

A directional reception beam in addition to a directional transmissionbeam may be used in order to increase beam efficiency. When adirectional reception beam is used, the directionality/orientation of atransmission beam and the directionality/orientation of the receptionbeam need to be aligned with each other. For example, even if a UE 1b-20 is located in the area of a transmission beam, if thedirectionality of a reception beam is not aligned with thedirectionality of the transmission beam, the UE may not receive thetransmission beam. Conversely, if the directionality of a transmissionbeam and the directionality of a reception beam are aligned with eachother, a UE 1 b-25 may transmit and receive data with a higherefficiency than when the reception beam is not used.

In order to detect a reception beam that is aligned with a transmissionbeam, the reception apparatus may apply different reception beams to thesame transmission beam so as to detect the reception beam providing thebest quality of reception. This process is referred to as reception beamsweeping.

A mobile communication system that uses a directional beam, an analogbeam, or a hybrid beam may transmit the common overhead signal in apreconfigured subframe via beam sweeping, and may perform user datatransmission and reception with a preconfigured UE using aunidirectional beam in another subframe.

FIG. 1C is a diagram illustrating the structure of a subframe of anext-generation mobile communication system according to an embodimentof the present disclosure.

Referring to FIG. 1C, a subframe 1 c-05 (overhead subframe (OSF)) thatincludes the overhead signal may be repeatedly transmitted at regularintervals 1 c-10. A single subframe includes a plurality of symbols, anda single directional beam is transmitted per symbol in an OSF. Forexample, a first symbol 1 c-15 of the OSF corresponds to t1, a secondsymbol 1 c-20 corresponds to t2, and an eleventh symbol 1 c-25corresponds to t11, and directional beams (or analog beams), which areconfigured to have the same beam width for each symbol, to coverdifferent areas, and to have directionality of different directions, maybe transmitted.

An overhead signal may be transmitted for each symbol of the OSF.

-   -   A signal for establishing downlink synchronization, such as a        primary synchronization signal (PSS), secondary synchronization        signal (SSS), or the like    -   A beam reference signal (BRS) for measuring a received signal        strength or a received signal quality for each beam    -   System information, a master information block (MIB) or a        physical broadcast channel (PBCH)    -   A PBCH includes information essential for a UE to access a        system, for example, a downlink beam bandwidth, a system frame        number, and the like

For reference, a public land mobile network (PLMN) identifier may bebroadcasted via a channel different from an MIB.

The same beam is transmitted in consecutive symbols of a subframedifferent from the periodically transmitted OSF, and user dataassociated with a preconfigured connected-state UE may be transmittedvia the beam. Hereinafter, the subframe different from the OSF isreferred to as a data subframe (DSF) 1 c-30.

FIG. 1D is a diagram illustrating a process in which frequency-basedpriority information for cell reselection is broadcasted via an SIB oris applied to a preconfigured UE via an RRC connection release message,which is dedicated RRC signaling, in a next-generation mobilecommunication system that uses a single beam according to an embodimentof the present disclosure, and is a diagram illustrating a method ofdetecting a suitable cell.

Referring to FIG. 1D, the UE may receive priority information for cellreselection in operation 1 d-10. The UE may receive, via a systeminformation block (SIB), priority information associated withfrequencies used in evolved universal mobile telecommunications system(UMTS) terrestrial radio access (EUTRA), and frequencies used in otherradio access technologies (RATs). However, priority informationassociated with all frequencies may not always be provided. The priorityinformation associated with the frequency of a service cell that a UEcurrently camps on may not be provided.

The UE may identify priority information in operation 1 d-15. Whenpriority information associated with the frequency of the currentserving cell is not provided, the UE proceeds with operation 1 d-20, andregards the priority of the frequency to be the lowest level. When thepriority information associated with the frequency of the currentserving cell is provided, the UE proceeds with operation 1 d-25.

The UE may apply priority information of each frequency in operation 1d-25. The priority information may be priority information that the UEreceives via the SIB.

When the UE receives a radio resource control (RRC) connection releasemessage from a base station, the UE may change from a connected mode toan idle mode. The RRC message may include frequency priorityinformation. This is UE-specific information, and may be preferentiallyapplied over frequency priority information provided via systeminformation (SIB). The system information is transmitted via a masterinformation block (MIB) and a system information block (SIB). The SIBmay be classified as SIB1, SIB2, SIB3, and the like depending on theinformation to transmit. A parameter related to cell reselection isincluded in SIB3, among them, and information associated withneighboring cells of the same frequency band is included in SIB4. The UEreceives SIB3 and SIB4, and receives a parameter related to cellreselection in the same frequency band. S-intrasearch information, whichdetermines whether to perform cell reselection on the basis of thestrength and quality of a signal, may be transmitted via the SIB 3.

The UE may determine whether frequency priority information is includedin the RRC message in operation 1 d-30. When it is determined thatfrequency priority information exists in the RRC message in operation 1d-30, the UE proceeds with operation 1 d-35. In operation 1 d-35, the UEapplies a T320 value, included in the RRC message, so as to drive asingle timer.

In operation 1 d-40, the UE may determine whether the current idle modestate is a “camped-on-any-cell state” or a “camped normally state”. Thatis, the UE determines whether the cell that the UE currently camps on isa suitable cell. The camped normally state indicates the state in whichthe UE camps on a suitable cell. A suitable cell is a cell that iscapable of providing normal service to a UE and satisfies the detailedconditions below.

-   -   A cell corresponds to a selected PLMN, a registered PLMN, or a        PLMN in an equivalent PLMN list    -   A cell that is not barred    -   A cell belonging to a PLMN that satisfies the above condition,        and belonging to at least one of the tracking areas (TAs) which        are not part of a TA list including forbidden TAs    -   A cell that satisfies a cell selection criterion    -   In the case of a closed subscriber group (CSG) cell, a cell of        which a CSG ID is included in a whitelist of a UE

The cell selection criterion indicates S-criteria, and the S-criteriamay be calculated using the equation below.Srxlev>0AND Squal>0

Here, Srxlev and Squal may be calculated as below.Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q_(rxlevminoffset))−Pcompensation−Qoffset_(temp)Squal=Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset))−Qoffset_(temp)

Q_(rxlevmeas) denotes a measured received strength, and Q_(qualmeas)denotes a measured received quality. Q_(rxlevmin) denotes the minimumpower value needed for operation, and Q_(qualmin) denotes the minimumquality value needed for operation. Q_(rxlevminoffset) denotes an offsetvalue of power for base stations with priority, Q_(qualminoffset)denotes an offset value of quality for base stations with priority, andPcompensation denotes a compensation parameter based on uplinktransmission power of a UE. Also, Qoffset_(temp) denotes an offset valueused when a UE fails to reestablish RRC connection (RRC connectionreestablishment failure).

The cell selection criterion may be applied to an initial cell selectionprocedure, in addition to a cell reselection procedure. That is, sincethe UE does not have information associated with an RF channel of anetwork, the UE may measure all RF channels that the UE can measure soas to detect the cell having the highest strength for each frequency.The UE may determine whether the cells satisfy the detailed conditions(whether a cell corresponds to a selected PLMN, a registered PLMN, or aPLMN included in an equivalent PLMN list, whether a cell is not barred,whether a cell belongs to a PLMN satisfying the above condition andbelongs to at least one of the TAs which are not part of a TA listincluding forbidden TAs, whether a cell satisfies a calculated cellselection criterion, and whether the CSG ID of a cell is included in awhitelist of a UE in the case of a CSG cell), and may detect a suitablecell.

The “camped-on-any-cell state” indicates the state in which the UE failsto camp on a suitable cell, and camps on an acceptable cell. For anacceptable cell, normal service is not allowed, and only emergency callsare allowed to the UE. An acceptable cell is a cell that satisfies theconditions below.

-   -   A cell that is not barred    -   A cell that satisfies a cell selection criterion

When the result of the determination in operation 1 d-40 shows that theUE is in the camped-on-any-cell state, the UE returns to operation 1d-25. The UE that returns to operation 1 d-25 may apply the frequencypriority information provided from the SIB, instead of the priorityinformation provided from the RRC connection release message. When theresult of the determination in operation 1 d-40 shows that the UE is inthe camped normally state, the UE proceeds with operation 1 d-45.

In operation 1 d-45, the UE determines whether a preconfigured conditionis satisfied. For example, the UE determines whether at least one of thefollowing three conditions is satisfied in operation 1 d-45. The threeconditions are as follows.

-   -   A UE is switched to a connected mode.    -   A T320 timer expires    -   A PLMN selection process is performed in response to a request        from a non-access stratum (NAS).

If any one of the conditions is satisfied, the UE proceeds withoperation 1 d-50. In operation 1 d-50, the priority information suppliedfrom the RRC connection release message is discarded. The UE returns tooperation 1 d-25, and applies the frequency priority informationprovided from the SIB. If a preconfigured condition is not satisfied inoperation 1 d-50 (e.g., if any one of the three conditions is notsatisfied), the UE proceeds with operation 1 d-55, and applies thepriority information provided from the RRC connection release message.

The frequency priority information may affect the UE's measurement of apreconfigured frequency. The UE always measures a frequency having ahigher priority than that of the current serving cell.

Conversely, the UE does not measure a frequency (intra-frequency) thatis the same as that of the serving cell or a frequency having a prioritythat is the same as, or lower than the priority of the frequency of theserving cell, for the economical use of power. Measurement may beperformed when the channel QoS of the serving cell is less than or equalto a preconfigured threshold value. The channel QoS may be determined onthe basis of Srxlev and Squal, and may be determined on the basis of apreconfigured function of reference signal received power (RSRP) orreference signal received quality (RSRQ). Cell reselection is performedfor movement to a cell having a better channel status. If the channelQoS of the current serving cell is good, there is no need to move to acell having a frequency of which the priority is the same as or lowerthan that of the current serving cell. Therefore, in order to reduce theamount of power consumed by unnecessary channel measurement, whether toperform measurement is determined on the basis of a preconfiguredthreshold value.

In the case of the same frequency (intra-frequency), if the QoS of theserving cell is the same as or lower than a preconfigured thresholdvalue Sintrasearch, channel measurement is performed with respect toother cells having the same frequency. In the case of differentfrequencies having the same or lower priority, if the QoS of the servingcell is the same as or lower than a preconfigured threshold valueSnonintrasearch, channel measurement is performed with respect to cellsof different frequencies. For the channel QoS, RSRP and RSRQ aregenerally taken into consideration. The channel QoS is determined on thebasis of Srxlev and Squal, and may be determined on the basis of apreconfigured function of RSRP or RSRQ.

While measurement is performed, if the channel QoS of a cell having ahigh-priority frequency is greater than a preconfigured threshold valueThreshX-high, the UE reselects the cell having the high-priorityfrequency as a serving cell. If the channel QoS of a cell having alow-priority frequency is greater than a preconfigured threshold valueThreshX-low and the QoS of the serving cell is lower thanThreshServing-low, the UE reselects the cell having the low-priorityfrequency as a serving cell. Cells having the same frequency or cellshaving frequencies of the same priority may be prioritized according toa preconfigured formula based on a channel QoS. This is referred to ascell ranking. The ranking value of a serving cell is defined to beRs=Q_(meas,s)+Q_(Hyst)−Qoffset_(temp). Conversely, the ranking value ofa neighboring cell is defined to beRn=Q_(meas,n)−Q_(offset)−Qoffset_(temp). Q_(meas,s) and Q_(meas,n)denote RSRP values of a serving cell and a neighboring cell. Q_(Hyst)denotes a hysteresis value applied to a serving cell. Q_(offset) denotesan offset value between a serving cell and a neighboring cell. Also,Qoffset_(temp) denotes an offset value used when a UE fails toreestablish RRC connection (RRC connection reestablishment failure). Inthe cell-ranking procedure, if the ranking value is high, acorresponding cell is selected as a serving cell.

FIG. 1E is a diagram illustrating a process in which frequency-basedpriority information for cell or beam reselection is broadcasted via anSIB or is applied to a preconfigured UE via an RRC connection releasemessage, which is dedicated RRC signaling, in a next-generation mobilecommunication system that uses a plurality of beams according to anembodiment of the present disclosure, and is a diagram illustrating amethod of detecting a suitable beam from among a plurality of beams.

Referring to FIG. 1E, the UE may receive priority information for cellor beam reselection in operation 1 e-10. The UE receives priorityinformation associated with frequencies used in EUTRA, and frequenciesused in other RATs, via an SIB. However, priority information associatedwith all frequencies may not always be provided. The priorityinformation associated with the frequency of a service cell that a UEcurrently camps on may not be provided. A plurality of beams may be usedin the next-generation mobile communication system, and thus priorityinformation associated with the plurality of beams may be provided. Eachof the plurality of beams may be identified on the basis of a beamidentity that indicates each beam. Also, priority information associatedwith the plurality of beams may not be provided. The priorityinformation associated with the plurality of beams is a subordinateconcept of priority information associated with the frequencies. If afrequency is determined on the basis of the priority informationassociated with the frequencies, priority information associated with aplurality of beams may be determined for the plurality of beams of thecorresponding frequency.

The UE identifies priority information in operation 1 e-15. If priorityinformation associated with the frequency of the current serving cell isnot provided, the UE proceeds with operation 1 e-20, and regards thepriority of the frequency to be the lowest level. In the same manner, ifpriority information associated with a serving beam of the currentserving cell is not provided, the UE regards the priority of the servingbeam to be the lowest level.

The UE may apply priority information of each frequency in operation 1e-25. The priority information may be cell and/or beam priorityinformation that the UE receives via an SIB. In the operation, thepriority information associated with a plurality of beams may beapplied.

If the UE receives an RRC connection release message from a basestation, the UE may change from a connected mode to an idle mode. TheRRC message may include frequency priority information. The RRC messagemay also include the priority information associated with a plurality ofbeams. This is UE-specific information, and may be preferentiallyapplied over frequency priority information or priority informationassociated with a plurality of beams provided via system information(SIB). The system information is transmitted via a master informationblock (MIB) and a system information block (SIB). The SIB may beclassified as SIB1, SIB2, SIB3, and the like depending on theinformation to transmit. A parameter related to cell reselection isincluded in SIB3 among them, and information associated with neighboringcells of the same frequency band is included in SIB4. SIB3 or SIB4 mayinclude information associated with a plurality of beams. Theinformation associated with the plurality of beams may include priorityinformation associated with the plurality of beams, beam identityinformation, beam pattern information, beam width information, beamstrength information, beam-related period information, beam offsetinformation, and the like. The UE receives SIB3 and SIB4, and mayreceive a parameter related to cell reselection in the same frequencyband or a parameter related to beam selection. S-intrasearchinformation, which determines whether to perform cell reselection on thebasis of the strength and quality of a signal, may be transmitted viaSIB 3. The S-intrasearch information may include information fordetermining whether to perform cell reselection on the basis of thestrength and quality of a signal at a frequency, and information fordetermining whether to perform beam reselection on the basis of thestrength and quality of a signal in a beam.

The UE may determine whether frequency priority information or priorityinformation associated with a plurality of beams exists in the RRCmessage in operation 1 e-30. If it is determined that the frequencypriority information or beam priority information exists in the RRCmessage in operation 1 e-30, the UE proceeds with operation 1 e-35. Inoperation 1 e-35, the UE applies a T320 value included in the RRCmessage so as to drive a single timer. In this operation, a separatetimer for a beam may be driven.

In operation 1 e-40, the UE may determine whether the current idle modestate corresponds to a “camped-on-any-cell state” or a “camped normallystate”. That is, the UE determines whether a cell or beam that the UEcurrently camps on is a suitable cell or beam. The “camped normallystate” indicates the state in which the UE camps on a suitable cell orcamps on a suitable beam. A suitable cell or a suitable beam indicates acell or a beam that is capable of providing normal service to a UE andsatisfies first conditions below.

-   -   A cell or beam corresponds to a selected PLMN, a registered        PLMN, or a PLMN in an equivalent PLMN list    -   A cell or beam that is not barred    -   A cell or beam belonging to a PLMN that satisfies the above        conditions and belonging to at least one of TAs which are not        part of a TA list including forbidden TAs.    -   A cell or beam that satisfies a cell selection criterion or beam        selection criterion    -   A cell or beam of which the CSG ID is included in the whitelist        of a UE in the case of a CSG cell

The cell selection criterion indicates S-criteria, and the S-criteriamay be calculated using the equation below.Srxlev>0AND Squal>0

Here, Srxlev and Squal may be calculated as below.Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q_(rxlevminoffset))−Pcompensation−Qoffset_(temp)Squal=Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset))−Qoffset_(temp)

Q_(rxlevmeas) denotes a measured received strength, and Q_(qualmeas)denotes a measured received quality. Q_(rxlevmin) denotes the minimumpower value needed for operation, and Q_(qualmin) denotes the minimumquality value needed for operation. Q_(rxlevminoffset) denotes an offsetvalue of power for base stations with priority, Q_(qualminoffset)denotes an offset value of quality for base stations with priority, andPcompensation denotes a compensation parameter based on uplinktransmission power of a UE. Also, Qoffset_(temp) denotes an offset valuethat is used when a UE fails to reestablish RRC connection (RRCconnection reestablishment failure). The cell selection criterion may beapplied to an initial cell selection procedure, in addition to a cellreselection procedure. That is, since the UE does not have informationassociated with an RF channel of a network, the UE may measure all RFchannels that the UE can measure so as to detect the cell having thehighest strength for each frequency. The UE may determine whether thedetailed conditions (whether a cell corresponds to a selected PLMN, aregistered PLMN, or a PLMN included in an equivalent PLMN list, whethera cell is not barred, whether a cell belongs to a PLMN satisfying theabove conditions and belongs to at least one of the TAs which are notpart of a TA list including forbidden TAs, whether a cell satisfies acalculated cell selection criterion, and whether the CSG ID of a cell isincluded in a whitelist of a UE in the case of a CSG cell) aresatisfied, and may detect a suitable cell.

The beam selection criterion indicates B-criteria, and the B-criteriamay be calculated using the equation below.Srxlev>0AND Squal>0

Here, Srxlev and Squal may be calculated as below.Srxlev=Q _(rxlevmeas,b)−(Q _(rxlevmin,b) +Q_(rxlevminoffset,b))−Pcompensation,b−Qoffset_(temp,b)Squal=Qy _(qualmeas,b)−(Q _(qualmin) +Q_(qualminoffset,b))−Qoffset_(temp,b)

The parameter may be a parameter associated with a beam. Q_(rxlevmeas,b)denotes a measured received strength, and Q_(qualmeas,b) denotes ameasured received quality. Q_(rxlevmin) denotes the minimum power valueneeded for operation, and Q_(qualmin) denotes the minimum quality valueneeded for operation. Q_(rxlevminoffset) denotes an offset value ofpower for base stations with priority or an offset value of power forbeams with priority. Q_(qualminoffset) denotes an offset value ofquality for base stations with priority or an offset value of power forbeams with priority. Also, Qoffset_(temp) denotes an offset value thatis used when a UE fails to reestablish RRC connection (RRC connectionreestablishment failure). Pcompensation is a compensation parameterbased on the uplink transmission power of a UE.

Pcompensation may take into consideration the beamforming capability ofa UE. For example, if the UE forms a narrow beam, the strength of areceived signal may increase, and accordingly, the UE may control thevalue of Pcompensation to be increased or decreased. That is,Pcompensation may be controlled in consideration of the beamformingcapability of the UE. The beamforming capability of the UE may includethe number of beams, a beam width, a beam gain, the maximum beam gain,an antenna pattern or antenna configuration, a beam orientation, theresolution of beamforming, the maximum transmission power, a beamsweeping length, and the like. New beamforming factors (UL beamformingfactors (UL BF factors)) may be defined to show the beamformingcapability of the UE as numerical values, and the beamforming factorvalues may be applied, whereby Pcompensation may be determined accordingto a function of the beamforming factor values. The beamformingcapability of the UE may be defined for each frequency band, and thebeamforming factors may be defined for each frequency band.

For example, Pcompensation may be determined to be f(P_(powerclass),P_(EMAX), UL BF factor), which is a function of P_(powerclass),P_(EMAX), and a UL BF factor, or may be determined to bef(P_(powerclass), P_(EMAX))−UL BF factor, which indicates subtractionbetween a P_(powerclass) P_(EMAX) function and a UL BF factor.P_(powerclass) denotes the maximum RF transmission power that the UE cantransmit. P_(EMAX) denotes the maximum uplink transmission power allowedin a cell that the UE camps on. The number of downlink reception beams(a reception beam width or a sweeping length) may be determined by acombination of a first parameter and a second parameter (or the lower ofthe two values).

-   -   The first parameter is information related to the number of        reception beams that a UE supports    -   The second parameter is an integer preconfigured for each        frequency band

According to an embodiment of the present disclosure, in order to applythe beamforming capability of the UE to a procedure for selecting asuitable beam, Pcompensation may be used, or a new factor (Newfactor)may be defined as below and additionally applied. The beamformingcapability of the UE may include the number of beams, a beam width, abeam gain, a maximum beam gain, an antenna pattern or antennaconfiguration, a beam orientation, the resolution of beamforming, amaximum transmission power, a beam sweeping length, and the like.Srxlev>0AND Squal>0

Here, Srxlev and Squal may be calculated as below.Srxlev=Q _(rxlevmeas,b)−(Q _(rxlevmin,b) +Q_(rxlevminoffset,b))−Pcompensation,b−Qoffset_(temp,b)−NewfactorSqual=Qy _(qualmeas,b)−(Q _(qualmin) +Q_(qualminoffset,b))−Qoffset_(temp,b)

That is, Newfactor may be adjusted in consideration of the beamformingcapability of the UE. New beamforming factors (UL beamforming factors)may be defined to show the beamforming capability of the UE as numericalvalues, and the beamforming factor values may be applied, wherebyNewfactor may be determined according to a function of the beamformingfactor values. The beamforming capability of the UE may be defined foreach frequency band, and the beamforming factors or Newfactor may bedefined for each frequency band. The number of downlink reception beams(a reception beam width or a sweeping length) may be determined by acombination of a first parameter and a second parameter (or the lower ofthe two values).

-   -   The first parameter is information related to the number of        reception beams that a UE supports    -   The second parameter is an integer preconfigured for each        frequency band

The beam selection criterion may be applied to an initial beam selectionprocedure, in addition to a beam reselection procedure. That is, sincethe UE does not have information associated with a radio-frequency (RF)channel of a network, the UE may measure all RF channels and all beamsthat the UE is capable of measuring, and may detect the beam having thehighest strength for each frequency or for each beam. The UE maydetermine whether the detailed conditions (whether a cell or beamcorresponds to a selected PLMN, a registered PLMN, or a PLMN included inan equivalent PLMN list, whether a cell or beam is not barred, whether acell or beam belongs to a PLMN satisfying the above conditions andbelongs to at least one of the TAs which are not part of a TA listincluding forbidden TAs, whether a cell or beam satisfies a calculatedcell selection criterion or beam selection criterion, and whether theCSG ID of a cell or beam is included in a whitelist of a UE in the caseof a CSG cell or beam) are satisfied, and may detect a suitable cell orbeam.

The “camped-on-any-cell state” indicates the state in which the UE doesnot camp on a suitable cell or suitable beam, but camps on an acceptablecell or an acceptable beam. In the acceptable cell or acceptable beam,normal service is not allowed, and only emergency calls are allowed tothe UE. The acceptable cell or acceptable beam may be a cell or beamthat satisfies the following conditions.

-   -   A cell or beam that is not barred    -   A cell or beam that satisfies a cell selection criterion or a        beam selection criterion

If the result of the determination in operation 1 e-40 shows that the UEis in the “camped-on-any-cell (or beam) state”, the UE returns tooperation 1 e-25. The UE that returns to operation 1 e-25 may apply thefrequency priority information or the priority information associatedwith the plurality of beams provided from the SIB, instead of thepriority information provided from the RRC connection release message.If the result of the determination in operation 1 e-40 shows that the UEis in the “camped normally state”, the UE proceeds with operation 1e-45.

In operation 1 e-45, the UE determines whether a preconfigured conditionis satisfied. For example, the UE determines whether at least one of thefollowing three conditions is satisfied in operation 1 e-45. The threeconditions are as follows.

-   -   A UE is switched to a connected mode.    -   A T320 timer expires    -   A PLMN selection process is performed in response to a request        from a NAS

If any one of the conditions is satisfied, the UE proceeds withoperation 1 e-50. In operation 1 e-50, the priority information suppliedfrom the RRC connection release message is discarded, and the UE returnsto operation 1 e-25 and applies the frequency priority information orthe priority information associated with the plurality of beams providedfrom the SIB. If a preconfigured condition is not satisfied in operation1 e-45 (e.g., if any one of the three conditions is not satisfied), theUE proceeds with operation 1 e-55, and applies the priority informationprovided from the RRC connection release message.

The frequency priority information may affect the UE's measurement of apreconfigured frequency. The UE may always measure a frequency having ahigher priority than that of the current serving cell (or beam).

Conversely, the UE does not measure a frequency (intra-frequency) thatis the same as that of the serving cell (or beam) or a frequency havinga priority that is the same as, or lower than, that of the serving cell,for the economical use of power. Measurement may be performed when thechannel QoS of the serving cell (or beam) is less than or equal to apreconfigured threshold value. The channel QoS is determined on thebasis of Srxlev and Squal, and may be determined on the basis of apreconfigured function of RSRP or RSRQ. Cell (or beam) reselection isperformed for movement to a cell (or beam) having a good channel status.If the channel QoS of the current serving cell (or beam) is good, thereis no need to move to a cell (or beam) having a frequency of the same orlower priority. Therefore, in order to reduce the amount of powerconsumed by unnecessary channel measurement, whether to performmeasurement is determined on the basis of a preconfigured thresholdvalue.

In the case of the same frequency (intra-frequency), if the QoS of theserving cell (or beam) is the same as or lower than a preconfiguredthreshold value Sintrasearch, channel measurement is performed withrespect to other cells (or beams) having the same frequency. In the caseof different frequencies having the same or lower priority, if the QoSof the serving cell (or beam) is the same as or lower than apreconfigured threshold value Snonintrasearch, channel measurement isperformed with respect to cells (or beams) of the different frequencies.For the channel QoS, RSRP and RSRQ are generally taken intoconsideration. The channel QoS is determined on the basis of Srxlev andSqual, and may be determined on the basis of a preconfigured function ofRSRP or RSRQ. While measurement is performed, if the channel QoS of acell (or beam) having a high-priority frequency is higher than apreconfigured threshold value ThreshX-high, the UE reselects the cell(or beam) having the high-priority frequency as a serving cell (orbeam). If the channel QoS of a cell (or beam) having a low-priorityfrequency is higher than a preconfigured threshold value ThreshX-low,and the QoS of the serving cell is lower than ThreshServing-low, the UEreselects the cell (or beam) having the low-priority frequency as aserving cell (or beam).

Cells having the same frequency or cells having frequencies of the samepriority may be prioritized according to a preconfigured formula basedon a channel QoS. This is referred to as cell ranking. The ranking valueof a serving cell is defined to beRs=Q_(meas,s)+Q_(Hyst)−Qoffset_(temp). Conversely, the ranking value ofa neighboring cell is defined to beRn=Q_(meas,n)−Qoffset−Qoffset_(temp). Q_(meas,s) and Q_(meas,n) denoteRSRP values of a serving cell and a neighboring cell. Q_(Hyst) denotes ahysteresis value applied to a serving cell. Qoffset denotes an offsetvalue between a serving cell and a neighboring cell. Also,Qoffset_(temp) denotes an offset value used when a UE fails toreestablish RRC connection (RRC connection reestablishment failure). Inthe cell-ranking procedure, if the ranking value is high, acorresponding cell is selected as a serving cell.

Beams having the same frequency or having frequencies of the samepriority may be prioritized according to a preconfigured formula basedon a channel QoS. This is referred to as beam ranking. The ranking valueof a serving beam may be defined to beRs,b=Q_(meas,s,b)+Q_(Hyst,b)−Qoffset_(temp,b)−BFfactor2. Conversely, theranking value of a neighboring beam is defined to beRn,b=Q_(meas,n,b)−Qoffset,b−Qoffset_(temp,b)−BFfactor3. Q_(meas,s,b) andQ_(meas,n,b) denote RSRP values of a serving cell and a neighboringcell. Q_(Hyst) denotes a hysteresis value applied to a serving cell.Qoffset denotes an offset value between a serving cell and a neighboringcell. Also, Qoffset_(temp) denotes an offset value used when a UE failsto reestablish RRC connection (RRC connection reestablishment failure).In the beam ranking procedure, if a ranking value is high, acorresponding beam is selected as a serving beam. BFfactor2 andBFfactor3 may be the same value, or may be different values. BFfactor2and BFfactor3 may be adjusted in consideration of the beamformingcapability of the UE. The beamforming capability of the UE may includethe number of beams, a beam width, a beam gain, the maximum beam gain,an antenna pattern or antenna configuration, a beam orientation, theresolution of beamforming, the maximum transmission power, and the like.New beamforming factors (UL beamforming factors) may be defined to showthe beamforming capability of the UE as numerical values, and thebeamforming factor values may be applied, whereby BFfactor2 andBFfactor3 may be determined according to the function of the beamformingfactor values. The beamforming capability of the UE may be defined foreach frequency band, and the beamforming factors may be defined for eachfrequency band.

FIG. 1F is a diagram illustrating a procedure of reselecting a suitablebeam in a next-generation mobile communication system that uses aplurality of beams according to an embodiment of the present disclosure.The operations of FIG. 1F may correspond to detailed operations ofoperation 1 e-40 of FIG. 1E.

Referring to FIG. 1F, FIG. 1F assumes an environment in which threetransmission and reception points (TRP) 1 f-02, 1 f-03, and 1 f-04around a UE 1 f-01 use a plurality of beams in a single cell. It isassumed that TRP1 1 f-02 and TRP2 1 f-03 use the same frequency band 1(FB1), and that TRP3 1 f-04 uses frequency band 2 (FB2) in the cell. TheUE 1 f-01 may perform RF channel scanning with respect only to somebands that satisfy a preconfigured condition from among all frequencybands of next-generation mobile communication system that the UE 1 f-01supports, or may perform RF channel scanning with respect to all bandsof the next-generation mobile communication system that the UE 1 f-01supports. The UE performs RF channel scanning such that a downlinkreception beam is formed to have a preconfigured beam width in apreconfigured direction, instead of performing downlink reception beamsweeping in order to detect a downlink reception beam that accords witha downlink transmission beam. If the UE 1 f-01 detects a carrier, the UE1 f-01 may select the beam that satisfies the beam selection criterionof the first conditions from among downlink beams of the correspondingcarrier, so as to receive system information. Subsequently, the UE 1f-01 determines whether the remaining first conditions are satisfied,and if the beam satisfies all of the first conditions, the UE 1 f-01selects the beam as a suitable beam and camps thereon.

For some reason, if the beam selection criterion of the UE 1 f-01 is notsatisfied, the UE 1 f-01 may perform beam reselection. The UE 1 f-01performs downlink synchronization with TRP1 1 f-02 and receives systeminformation.

In operation 1 f-05, the UE 1 f-01 measures a beam reference signal. TheUE 1 f-01 measures beam reference signals for respective downlink beamsin a subframe (overhead subframe (OSF) 1 c-05 of FIG. 1C), whichincludes an overhead signal and is repeatedly transmitted at regularintervals.

In operation 1 f-10, the UE 1 f-01 calculates Srxlev and Squal so as todetermine whether each beam satisfies the beam selection criterion onthe basis of the measurement of a beam reference signal. Also, the UE 1f-01 determines whether a suitable beam exists on the basis of thecalculation of Srxlev and Squal.

In the process of calculating Srxlev and Squal, Pcompensation may bedetermined in consideration of the beamforming capability of the UE 1f-01. The beamforming capability of the UE 1 f-01 may include the numberof beams, a beam width, a beam gain, the maximum beam gain, an antennapattern or antenna configuration, a beam orientation, the resolution ofbeamforming, the maximum transmission power, a beam sweeping length, andthe like. New beamforming factors (UL beamforming factors (UL BFfactors)) may be defined to show the beamforming capability of the UE 1f-01 as numerical values, and the beamforming factor values may beapplied, whereby Pcompensation may be determined according to a functionof the beamforming factor values. The beamforming capability of the UE 1f-01 may be defined for each frequency band, and the beamforming factorsmay be defined for each frequency band. For example, Pcompensation maybe determined to be f(P_(powerclass), P_(EMAX), UL BF factor), which isa function of P_(powerclass), P_(EMAX), and a UL BF factor, or may bedetermined to be f(P_(powerclass), P_(EMAX))−UL BF factor, whichindicates subtraction between a P_(powerclass) P_(EMAX) function and aUL BF factor. P_(powerclass) denotes the maximum RF transmission powerthat the UE can transmit. P_(EMAX) denotes the maximum uplinktransmission power allowed in a cell that the UE camps on.

In operation 1 f-10, the UE 1 f-01 determines Pcompensation by takinginto consideration the beamforming capability of the UE 1 f-01 asdescribed above, and calculates Srxlev and Squal so as to determinewhether a suitable beam exists from among beams measured in operation 1f-05. If a suitable beam exists, the UE 1 f-01 may camp on theidentified suitable beam.

When it is determined that a suitable beam does not exist, the UE 1 f-01performs downlink synchronization with another TRP again, and receivessystem information. For example, the UE 1 f-01 performs downlinksynchronization with TRP2 1 f-03 and receives system information.

In operation 1 f-05, the UE 1 f-01 measures a beam reference signal. TheUE 1 f-01 measures beam reference signals for respective downlink beamsin a subframe (overhead subframe (OSF) 1 c-05 of FIG. 1C) that includesan overhead signal and is repeatedly transmitted at regular intervals.

In operation 1 f-20, the UE 1 f-01 calculates Srxlev and Squal so as todetermine whether each beam satisfies the beam selection criterion onthe basis of the measurement of a beam reference signal. Also, the UE 1f-01 determines whether a suitable beam exists on the basis of thecalculation of Srxlev and Squal. In the process of calculating Srxlevand Squal, Pcompensation may be determined in consideration of thebeamforming capability of the UE 1 f-01. As described in operation 1f-10, the UE 1 f-01 determines Pcompensation by taking intoconsideration the beamforming capability of the UE 1 f-01, andcalculates Srxlev and Squal, so as to determine whether a suitable beamexists from among beams measured in operation 1 f-15. If a suitable beamexists, the UE 1 f-01 may camp on the identified suitable beam.

When it is determined that a suitable beam does not exist, the UE 1 f-01performs downlink synchronization with another TRP again, and receivessystem information. For example, the UE 1 f-01 performs downlinksynchronization with TRP3 1 f-04 and receives system information.

In operation 1 f-25, the UE 1 f-01 measures a beam reference signal. TheUE 1 f-01 measures beam reference signals for respective downlink beamsin a subframe (overhead subframe (OSF) 1 c-05 of FIG. 1C) that includesan overhead signal and is repeatedly transmitted at regular intervals.

In operation 1 f-30, the UE 1 f-01 calculates Srxlev and Squal so as todetermine whether each beam satisfies the beam selection criterion onthe basis of the measurement of a beam reference signal. Also, the UE 1f-01 determines whether a suitable beam exists on the basis of thecalculation of Srxlev and Squal.

In the process of calculating Srxlev and Squal, Pcompensation may bedetermined in consideration of the beamforming capability of the UE 1f-01. In operation 1 f-30, the UE 1 f-01 determines Pcompensation byapplying UL BF factors which are different depending on a frequency bandsince TRP3 1 f-04 uses frequency band 2 (FB2), which is different fromthe frequency band of TRP1 1 f-02 and TRP2 1 f-03. The UL BF factors maybe factors that quantify the beamforming capability of a UE, such as thenumber of beams, a beam width, a beam gain, the maximum beam gain, anantenna pattern or antenna configuration, a beam orientation, theresolution of beamforming, the maximum transmission power, a beamsweeping length, and the like, as described in operation 1 f-10, and maybe different depending on a frequency band. In operation 1 f-30,Pcompensation is determined in consideration of the beamformingcapability of the UE, and Srxlev and Squal are calculated so as todetermine whether a suitable beam exists from among beams measured inoperation 1 f-25. If a suitable beam exists, the UE 1 f-01 may camp onthe identified suitable beam in operation 1 f-35. If a suitable beamdoes not exist, the UE performs downlink synchronization with anotherTRP and receives system information again, as described above.

FIG. 1G is a block diagram of the structure of a UE according to anembodiment of the present disclosure.

Referring to FIG. 1G, the UE may include a radio-frequency (RF)processor 1 g-10, a baseband processor 1 g-20, a storage unit 1 g-30,and a controller 1 g-40.

The RF processor 1 g-10 performs a function for transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 1 g-10 up-convertsa baseband signal provided from the baseband processor 1 g-20 into an RFband signal, transmits the RF band signal via an antenna, anddown-converts the RF band signal received via the antenna into abaseband signal. For example, the RF processor 1 g-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. Although only a single antenna isillustrated in the drawing, the UE may include a plurality of antennas.In addition, the RF processor 1 g-10 may include a plurality of RFchains. Moreover, the RF processor 1 g-10 may perform beamforming. Forthe beamforming, the RF processor 1 g-10 may control the phase and thesize of each signal transmitted/received via a plurality of antennas orantenna elements. Also, the RF processor may perform MIMO, and mayreceive a plurality of layers while performing a MIMO operation. The RFprocessor 1 g-10 may appropriately configure a plurality of antennas orantenna elements according to the control of the controller so as toperform reception beam sweeping, or may control the orientation of areception beam and a beam width such that a reception beam accords witha transmission beam.

The baseband processor 1 g-20 performs a function for conversion betweena baseband signal and a bitstream according to the physical layerstandard of the system. For example, in the case of data transmission,the baseband processor 1 g-20 generates complex symbols by encoding andmodulating a transmission bitstream. Further, in the case of datareception, the baseband processor 1 g-20 reconstructs a receptionbitstream by demodulating and decoding a baseband signal provided fromthe RF processor 1 g-10. For example, according to anorthogonal-frequency-division-multiplexing (OFDM) scheme, in the case ofdata transmission, the baseband processor 1 g-20 generates complexsymbols by encoding and modulating a transmission bitstream, maps thecomplex symbols to subcarriers, and then configures OFDM symbols via aninverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP)insertion. Further, in the case of data reception, the basebandprocessor 1 g-20 divides the baseband signal provided from the RFprocessor 1 g-10 into OFDM symbol units, reconstructs the signals mappedto the subcarriers via a fast Fourier transform (FFT) operation, andthen reconstructs a reception bitstream via demodulation and decoding.

The baseband processor 1 g-20 and the RF processor 1 g-10 transmit andreceive a signal, as described above. Accordingly, each of the basebandprocessor 1 g-20 and the RF processor 1 g-10 may be referred to as atransmitter, a receiver, a transceiver, or a communication unit. Inaddition, at least one of the baseband processor 1 g-20 or the RFprocessor 1 g-10 may include a plurality of communication modules so asto support many different radio access technologies. In addition, atleast one of the baseband processor 1 g-20 or the RF processor 1 g-10may include different communication modules to process signals ofdifferent frequency bands. For example, the different radio accesstechnologies may include an LTE network, an NR network, and the like.Further, the different frequency bands may include a super-highfrequency (SHF) (e.g., 2.5 GHz and 5 GHz) band and a millimeter (mm)wave (e.g., 60 GHz) band.

The storage unit 1 g-30 stores data such as a basic program, anapplication program, and configuration information for the operation ofthe UE. The storage unit 1 g-30 may provide stored data in response to arequest from the controller 1 g-40.

The controller 1 g-40 controls the overall operation of the UE. Forexample, the controller 1 g-40 transmits and receives a signal via thebaseband processor 1 g-20 and the RF processor 1 g-10. Also, thecontroller 1 g-40 writes and reads data to/from the storage unit 1 g-40.To this end, the controller 1 g-40 may include at least one processor.For example, the controller 1 g-40 may include a communication processor(CP), which performs control for communication, and an applicationprocessor (AP), which controls a higher layer such as an applicationprogram. The controller 1 g-40 may include a baseband processor 1 g-42.

According to an embodiment of the present disclosure, the controller 1g-40 may perform control so as to receive system information includingfirst beam reselection priority information, to receive a radio resourcecontrol (RRC) message including second beam reselection priorityinformation, to determine whether the UE camps on a suitable beam, andto apply one of the first beam reselection priority information and thesecond beam reselection priority information on the basis of the resultof the determination.

Also, the controller 1 g-40 may perform control so as to determinewhether the UE camps on a suitable beam on the basis of the beamformingcapability of the UE. The beamforming capability of the UE correspondsto at least one beamforming factor, and may be defined for eachfrequency band. Also, the beamforming capability of the UE may includeat least one of the number of beams, a beam width, a beam gain, themaximum beam gain, an antenna pattern, a beam orientation, theresolution of beamforming, the maximum transmission power, or a beamsweeping length.

If the UE does not camp on a suitable beam, the controller 1 g-40 mayperform control so as to apply the first beam reselection priorityinformation. If the UE camps on a suitable beam, the controller 1 g-40performs control so as to apply the second beam reselection priorityinformation. Also, if the UE camps on a suitable beam and apreconfigured condition is satisfied, the controller 1 g-40 may performcontrol so as to delete the second beam reselection priorityinformation.

Also, the controller 1 g-40 may control the operation of the UEaccording to the first embodiment of the present disclosure. Thecontroller 1 g-40 may control the operation of the UE as described withreference to FIGS. 1A to 1F.

FIG. 1H is a block diagram of a TRP in a wireless communication systemaccording to an embodiment of the present disclosure. A base station mayinclude at least one TRP.

Referring to FIG. 1H, the base station may include an RF processor 1h-10, a baseband processor 1 h-20, a communication unit 1 h-30, astorage unit 1 h-40, and a controller 1 h-50.

The RF processor 1 h-10 performs a function for transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 1 h-10 up-convertsa baseband signal provided from the baseband processor 1 h-20 into an RFband signal and then transmits the converted signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal. For example, the RF processor 1 h-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although only a single antenna is illustrated in thedrawing, a first access node may include a plurality of antennas. Inaddition, the RF processor 1 h-10 may include a plurality of RF chains.Moreover, the RF processor 1 h-10 may perform beamforming. For thebeamforming, the RF processor 1 h-10 may control the phase and the sizeof each of the signals transmitted and received via a plurality ofantennas or antenna elements. The RF processor may perform downlink MIMOoperation by transmitting one or more layers.

The baseband processor 1 h-20 performs a function of converting betweena baseband signal and a bitstream according to the physical layerstandard of a first radio access technology. For example, in the case ofdata transmission, the baseband processor 1 h-20 generates complexsymbols by encoding and modulating a transmission bitstream. Further, inthe case of data reception, the baseband processor 1 h-20 reconstructs areception bitstream by demodulating and decoding a baseband signalprovided from the RF processor 1 h-10. For example, according to an OFDMscheme, in the case of data transmission, the baseband processor 1 h-20generates complex symbols by encoding and modulating the transmissionbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols via an IFFT operation and CP insertion. Also, in the caseof data reception, the baseband processor 1 h-20 divides a basebandsignal provided from the RF processor 1 h-10 into OFDM symbol units,restores signals mapped onto the subcarriers via the FFT operation, andrestores a received bitstream via demodulation and decoding. Thebaseband processor 1 h-20 and the RF processor 1 h-10 transmit andreceive a signal as described above. Accordingly, each of the basebandprocessor 1 h-20 and the RF processor 1 h-10 may be referred to as atransmitter, a receiver, a transceiver, a communication unit, or awireless communication unit.

The communication unit 1 h-30 provides an interface for performingcommunication with other nodes in a network. The communication unit 1h-30 may be referred to as “backhaul communication unit”.

The storage unit 1 h-40 may store data, such as a basic program, anapplication program, configuration information, or the like, used foroperating the main base station. Particularly, the storage unit 1 h-40may store information associated with a bearer allocated to a connectedUE, a measurement result reported from a connected UE, and the like.Also, the storage unit 1 h-40 may store information which is a criterionto determine whether to provide or interrupt multiple access to a UE.The storage unit 1 h-40 may provide stored data in response to a requestfrom the controller 1 h-50.

The controller 1 h-50 may control the overall operation of the main basestation. For example, the controller 1 h-50 may transmit and receive asignal via the baseband processor 1 h-20 and the RF processor 1 h-10, orvia the backhaul communication unit 1 h-30. Also, the controller 1 h-50writes and reads data to/from the storage unit 1 h-40. To this end, thecontroller 1 h-50 may include at least one processor. The controller 1h-50 may include a baseband processor 1 h-52. Also, the controller 1h-50 may control the operation of the base station or TRP according tothe first embodiment of the present disclosure. The controller 1 h-50may control the operations of the base station or TRP which have beendescribed with reference to FIGS. 1A to 1F.

Second Embodiment

FIG. 2A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 2A, a radio access network of the next-generationmobile communication system includes a new radio node B (hereinafterreferred to as NR NB or a base station) 2 a-10 and a new radio corenetwork (NR CN) 2 a-05, as illustrated in the drawing. A new radio userequipment (NR UE or UE) 2 a-15 may access an external network via the NRNB 2 a-10 and the NR CN 2 a-05.

In FIG. 2A, the NR NB 2 a-10 may correspond to an evolved node B (eNB)in the legacy LTE system. The NR NB is connected to the NR UE 2 a-15 viaa radio channel, and may provide better service than the legacy node B.In the next-generation mobile communication system, all user traffic isserviced via a shared channel, and thus a device that collects statusinformation of UEs, such as a buffer status, an available transmissionpower status, a channel status or the like, and performs scheduling isneeded, and the NR NB 2 a-10 takes charge of the same. One NR NBgenerally controls a plurality of cells. In order to implementhigh-speed data transmission compared to legacy LTE, a bandwidth greaterthan or equal to the maximum legacy bandwidth may be needed, orthogonalfrequency division multiplexing (OFDM) is used as a radio accesstechnology, and beamforming technology is additionally used. Further, anadaptive modulation and coding (hereinafter, referred to as AMC) scheme,which determines a modulation scheme and a channel coding rate accordingto the channel status of the UE, is applied to the LTE system. The NR NBmay include one or more TRPs and a single central device. The TRP is adevice for transmitting and receiving a radio signal, and the centraldevice is a device that takes charge of an RRC function such as mobilitymanagement or connection management associated with a UE.

The NR CN 2 a-05 supports mobility, configures a bearer, or configuresQoS. The NR CN is a device that is in charge of various controlfunctions in addition to a mobility management function associated witha UE, and may be connected to a plurality of node Bs. Also, thenext-generation mobile communication system may interoperate with thelegacy LTE system, and the NR CN may be connected to the MME 2 a-25 viaa network interface. The MME is connected to an eNB 2 a-30, which is thelegacy node B.

The NR is aimed at supporting a faster data transmission speed thanlegacy LTE. As a method of increasing the data transmission speed in theNR, a method is being considered in which a signal is transmitted usinga wide frequency band existing in a frequency band greater than or equalto 6 GHz. That is, it is being considered to use a millimeter wave(hereinafter mmWave) band, such as a 28 GHz band, a 60 GHz band, or thelike, in order to increase a transmission rate. In a frequency band,which is considered for a mmWave band, signal attenuation per distanceis relatively large, and thus, transmission on the basis of adirectional beam generated using multiple antennas is required in orderto secure coverage. In the case of directional-beam-based transmission,transmission or reception of a signal may be difficult at a locationwhere a beam is not formed. In order to overcome the above-describeddrawback, beam sweeping is used. Beam sweeping is a scheme in which atransmission apparatus sequentially sweeps or rotates and transmitsdirectional beams having a preconfigured beam width, such that a beam isreceived by a reception apparatus which exists within a beam range ofthe transmission apparatus.

FIG. 2B is a diagram illustrating beam sweeping of a next-generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 2B, for example, a transmission reception point (TRP)2 b-05 (a device for transmitting and receiving a radio signal in anetwork, an NR NB, or a device connected to an NR NB) transmits adirectional beam having a preconfigured width at a preconfigured pointin time t1 in a preconfigured direction, and transmits a directionalbeam having the same width at t2 in another direction, and so on,whereby the beams are transmitted in all directions during apreconfigured period of time. Accordingly, a downlink signal transmittedby a base station arrives at a UE 2 b-15 at t9, and arrives at a UE 2b-10 at t4.

The beam sweeping is mainly used when a base station does not know theorientation of a directional beam to be applied to a UE, and a commonoverhead signal to be transmitted to an idle-state UE may be transmittedvia beam sweeping.

A directional reception beam, in addition to a directional transmissionbeam, may be used in order to increase beam efficiency. When adirectional reception beam is used, the directionality/orientation of atransmission beam and the directionality/orientation of the receptionbeam need to be aligned with each other. For example, although a UE 2b-20 is located in the area of a transmission beam, if thedirectionality of a reception beam is not aligned with thedirectionality of the transmission beam, the UE may not receive thetransmission beam. Conversely, if the directionality of a transmissionbeam and the directionality of a reception beam are aligned with eachother, a UE 2 b-25 may transmit and receive data with higher efficiencythan when the reception beam is not used.

In order to detect a reception beam that accords with a transmissionbeam, a reception apparatus may sequentially rotate the directionalityof a reception beam with respect to the same transmission beam so as todetect the reception beam providing best quality of reception. Thisprocess is referred to as reception beam sweeping.

A mobile communication system that uses a directional beam, an analogbeam, or a hybrid beam may transmit the common overhead signal in apreconfigured subframe via beam sweeping, and may perform transmissionand reception of user data with a preconfigured UE using aunidirectional beam in another subframe.

FIG. 2C is a diagram illustrating the structure of a subframe of anext-generation mobile communication system according to an embodimentof the present disclosure.

Referring to FIG. 2C, a subframe 2 c-05 (overhead subframe (OSF)) thatincludes an overhead signal may be repeatedly transmitted at regularintervals 2 c-10. A single subframe includes a plurality of symbols, anda single directional beam is transmitted per symbol in an OSF. Forexample, a first symbol 2 c-15 of the OSF corresponds to t1, a secondsymbol 2 c-20 corresponds to t2, and an eleventh symbol 2 c-25corresponds to t11, and directional beams (or analog beams), which areconfigured to have the same beam width for each symbol, to coverdifferent areas, and to have directionality of different directions, maybe transmitted.

An overhead signal below may be transmitted for each symbol of the OSF.

-   -   A signal for establishing downlink synchronization, such as a        primary synchronization signal (PSS), secondary synchronization        signal (SSS), or the like    -   A beam reference signal (BRS) that is capable of measuring a        received signal strength or a received signal quality for each        beam    -   System information, a master information block (MIB) or physical        broadcast channel (PBCH)

The PBCH includes information essential for a UE to access a system, forexample, a downlink beam bandwidth, a system frame number, and the like

The PBCH may be transmitted, including a first parameter related toreception beam configuration of a UE.

For reference, preconfigured system information (e.g., random accessresource information or the like) may be transmitted via anothersubframe, as opposed to a subframe in which a PSSS/SSS is transmitted.

The same beam is transmitted in consecutive symbols in a subframedifferent from the periodically transmitted OSF, and user dataassociated with a preconfigured connected-state UE may be transmittedvia the beam. Hereinafter, the subframe different from the OSF isreferred to as a data subframe (DSF) 2 c-30.

A UE needs to continuously measure and evaluate the receivedstrength/quality of a downlink transmission beam when performing an idlestate operation and a connected state operation (hereinafter, thereceived quality in the present disclosure indicates both receivedstrength (received power) and received quality). In the analog/hybridbeam system, the received quality of a downlink transmission beam may bedifferent on the basis of a downlink reception beam configuration (thedownlink reception beam configuration indicates thedirectionality/orientation of a downlink reception beam, a width, anangle, the number of beams needed to cover all directions, a beamsweeping length, and the like). For example, even if the same downlinktransmission beam is used, if a reception beam of 15 degrees is used,better received quality may be obtained compared to the case of using areception beam of 30 degrees. That is, the received quality may bedifferent depending on the width of a received beam. If the width of areceived beam is narrow, a relatively better received quality may beobtained. Conversely, if a reception beam of 30 degrees is used, thetransmission beam needs to be received 12 times in order to recognizethe beam orientation that provides the best quality. If a reception beamof 15 degrees is used, the transmission beam needs to be received 24times.

An idle-state UE needs to measure the quality of a current servingdownlink transmission beam once at least every discontinuous receptioninterval. The serving downlink transmission beam indicates the downlinktransmission beam that the UE camps on or via which the UE is receivingdata. Depending on the reception beam configuration that the UE applies,the amount of time and the amount of charge of a battery spent formeasuring the quality of a transmission beam may be different. Forexample, if the UE applies reception beam configuration 1 (aconfiguration that needs to perform reception beam sweeping 24 times inorder to cover all directions, a range of 360 degrees, i.e., a downlinkreception beam configuration that performs sweeping of a downlinkreception beam having a width of 15 degrees in a preconfigureddirection), 24 units of time may be spent for measuring the quality of aserving downlink transmission beam. If the UE applies reception beamconfiguration 2 (a configuration that needs to perform reception beamsweeping 4 times in order to cover all directions, a range of 360degrees, i.e., a downlink reception beam configuration that performssweeping of a downlink reception beam having a width of 90 degrees in apreconfigured direction), only 4 units of time may be spent measuringthe serving downlink transmission beam. A unit of time is an intervalbetween the same transmission beam, or a transmission beam transmissioninterval, or an OSF interval.

The downlink reception beam configuration of the UE is related to thecapability of the UE. The number of reception beams or the width of areception beam that is needed to cover all directions may be determinedby an antenna element/array included in the UE. A high-performance UEcovers all directions using a larger number of reception beams, and mayhave high reception performance. A low-performance UE covers a smallernumber of reception beams and may have low reception performance.

The major role of an idle-state UE is to detect whether paging occurs,and high reception performance may not be needed to receive a pagingmessage. If a high-performance UE spends 24 units of time for singlemeasurement of a downlink transmission beam only for receiving pagingwell, this may result in insignificant improvement in performance andsignificant battery charge expense. In addition, when idle-state UEsmeasure a serving cell/beam, if the amount of time spent for themeasurement is different depending on the performance of a UE, it isdifficult to guarantee consistent performance of the system as a whole.

In order to overcome the above-described problem, in the secondembodiment of the present disclosure, an idle-state UE applies apreconfigured common configuration when measuring a downlink receptionbeam, and a connected-state UE applies a preconfigured dedicatedconfiguration. A UE determines the common configuration by taking intoconsideration the UE's capability and reference configurationinformation associated with a TRP/cell/frequency/frequency band, anddetermines the dedicated configuration by taking into consideration theUE's capability, or as indicated by a dedicated message from a basestation.

FIG. 2D is a diagram illustrating the overall operation according to anembodiment of the present disclosure.

Referring to FIG. 2D, in a mobile communication system including a UE 2d-05 and at least one TRP 2 d-10 and 2 d-15, TRP0 2 d-10 and TRP1 2 d-15transmit OSFs at regular intervals.

In operation 2 d-25, the UE 2 d-05 receives a PSS/SSS of an OSFtransmitted from the TRP0 2 d-10, and establishes downlinksynchronization.

In operation 2 d-27, the UE 2 d-05 may receive preconfigured systeminformation in the OSF. The system information may include referenceconfiguration information (or parameter 1).

In operation 2 d-28, the UE 2 d-05 may determine a common downlinkreception beam configuration on the basis of the reference configurationinformation. The common downlink reception beam configuration may bereferred to as a common reception beam configuration, first receptionbeam configuration, first common reception beam configuration, or thelike. For example, the UE 2 d-05 may take into consideration thereference configuration information and the capability of the UE 2 d-05,and may determine the common downlink reception beam configuration to bethe lower value therebetween.

The scope of the reference configuration information may include a TRP,a cell, and a frequency or frequency band. If the scope is a TRP, the UE2 d-05 may take into consideration the reference configurationinformation when receiving or measuring a downlink transmission beam ofthe OSF in which the system information is received. If the scope is acell, the UE 2 d-05 may take into consideration the referenceconfiguration information when receiving or measuring a downlinktransmission beam of a cell in which the system information is received.If the scope is a frequency, the UE 2 d-05 may take into considerationthe reference configuration information when receiving or measuring adownlink transmission beam of a frequency at which the systeminformation is received. If the scope is a frequency band, the UE 2 d-05may take into consideration the reference configuration information whenreceiving or measuring a downlink transmission beam of a frequency bandin which the system information is received.

In operation 2 d-30, the UE 2 d-05 measures a beam reference signal. TheUE 2 d-05 may measure the beam reference signal on the basis of thecommon downlink reception beam. The UE 2 d-05 may measure the qualityand the strength of a beam reference signal by applying the determineddownlink reception beam configuration.

In operation 2 d-35, the UE 2 d-05 may determine a beam to camp on, onthe basis of the measurement result, and may camp on the determinedbeam. The UE 2 d-05 may camp on the downlink transmission beam havingthe best signal quality, for example, transmission beam 0, from among aplurality of transmission beams of the TRP0 2 d-10. “Camping on a beam”means receiving remaining system information at the beam and monitoringa paging channel at the beam.

In operation 2 d-40, the UE 2 d-10 may monitor a paging channeltransmitted via the downlink transmission beam. In other words, the UE 2d-05 may determine whether a paging message is received via the pagingchannel. In this instance, the downlink reception beam commonconfiguration determined in operation 2 d-28 is applied.

If a preconfigured condition is satisfied, for example, if the receivedquality of a serving downlink transmission beam is less than or equal toa preconfigured reference, the UE 2 d-05 initiates measurement of aneighboring TRP. In this instance, the UE 2 d-05 may measure theneighboring TRP by applying the downlink reception beam commonconfiguration determined in operation 2 d-28. In other words, the UE 2d-05 explores a PSS/SSS by applying the downlink reception beam commonconfiguration, establishes downlink synchronization, and receives adownlink transmission beam by applying different reception beamdirectionality/orientations the number of times defined in the downlinkreception beam common configuration when measuring the received qualityof a beam reference signal of the preconfigured downlink transmissionbeam.

In operation 2 d-45, the UE 2 d-05 may establish downlinksynchronization with TRP1 2 d-15. In operation 2 d-50, the UE 2 d-05 mayreceive beam reference signals in an OSF of TRP1 2 d-15, and determinesthe received quality of each beam.

If a beam that satisfies a preconfigured reference exists among downlinktransmission beams of the TRP1 2 d-15, the UE 2 d-05 camps on the beam(e.g., a transmission beam 10) in operation 2 d-55. The UE 2 d-05 maymonitor a paging channel in the beam that the UE2 d-05 camps on.

At any point in time, the UE 2 d-05 may need to set up an RRCconnection. When it is necessary to set up an RRC connection, the UE 2d-05 requests RRC connection establishment in operation 2 d-60. Forexample, if the UE 2 d-05 receives a paging message, a higher-layerdevice of the UE 2 d-05 may direct an access-layer device of the UE 2d-05 to set up an RRC connection.

In operation 2 d-65, the UE 2 d-05 may perform a random access procedurein the current serving beam or serving cell. Via the random accessprocedure, the UE 2 d-05 may inform TRP1 2 d-15 of the downlinktransmission beam (or serving downlink transmission beam) having thebest received quality.

In operation 2 d-70, the UE 2 d-05 transmits an RRC connection setuprequest message to a central unit 2 d-20, and the central unit 2 d-20indicates an RRC connection configuration to the UE 2 d-05.

The UE 2 d-05 that sets up the RRC connection may report, to the CU 2d-20, the capability of the UE 2 d-05 (UE capability), for example,downlink reception beam configuration capability, in operation 2 d-72.That is, the UE 2 d-05 may report UE capability information. On thebasis of the information, the CU 2 d-20 may be aware of the downlinkreception beam configuration that the UE currently uses. If it ispossible to use a reception beam narrower than the current receptionbeam configuration, the CU 2 d-20 may determine to refine a downlinkreception beam of the UE 2 d-05. The CU 2 d-20 may direct the TRP1 2d-15 to perform a downlink reception beam refinement procedure.

In operation 2 d-75, TRP1 2 d-15 and the UE 2 d-05 may perform thedownlink reception beam refinement procedure. Via the process, the TRP12 d-15 repeatedly transmits a serving downlink transmission beam to theUE 2 d-05, and the UE 2 d-05 performs sweeping of a reception beamwithin a limited range, and identifies the downlink reception beamhaving the best reception signal. In this instance, the newly determineddownlink reception beam may be configured on the basis of the dedicatedconfiguration of the UE 2 d-05. The dedicated configuration may bereferred to as a downlink dedicated reception beam configuration, asecond reception beam configuration, a refined reception beamconfiguration, and the like. The dedicated configuration of the UE 2d-05 may be configured on the basis of the maximum performance of theUE. For example, a UE that is capable of configuring a total of 24reception beams to cover all directions may set the internal angle of adownlink reception beam to 15 degrees, and may set a reception beamsweeping length to 24. A UE that is capable of configuring a total of 12reception beams to cover all directions may set the internal angle of adownlink reception beam to 30 degrees, and may set a reception beamsweeping length to 12.

The UE 2 d-05 may perform radio link monitoring (operation 2 d-80), datareception (operation 2 d-85), and channel status monitoring (operation 2d-90) by applying the dedicated downlink reception beam configured asdescribed above.

Radio link monitoring is monitoring the status of the current radio linkof the UE 2 d-05, and on the basis of the strength/quality of areference signal of the current downlink transmission beam, the UE 2d-05 may determine whether smooth service is allowed in thecorresponding beam. In this instance, the UE 2 d-05 may determine thequality of a serving downlink transmission beam by applying the downlinkreception beam dedicated configuration (or using a downlink receptionbeam formed by applying the downlink reception beam dedicatedconfiguration).

The UE 2 d-05 may receive downlink data via the serving downlinktransmission beam. In this instance, the downlink reception beamdedicated configuration is applied (or a downlink reception beam is usedthat is formed by applying the downlink reception beam dedicatedconfiguration).

The UE 2 d-05 may monitor the received quality of a preconfiguredreference signal, for example, a channel status indication referencesignal, or downlink data via the serving downlink transmission beam, andmay report the result of monitoring to a TRP via a preconfigured uplinkchannel. In this instance, the UE 2 d-05 may apply the downlinkreception beam dedicated configuration (or use a downlink reception beamformed by applying the downlink reception beam dedicated configuration)when measuring the quality of the reference signal.

As described above, the UE 2 d-05 may use a reception beam formed byapplying the downlink reception beam common configuration in operations2 d-28 to 2 d-72, and may use a reception beam formed by applying thedownlink reception beam dedicated configuration in operations 2 d-75 to2 d-90.

FIG. 2E is a diagram illustrating a reception beam configuration of a UEaccording to an embodiment of the present disclosure.

The reception beam configuration may indicate the width/coverage/angleor the like of a reception beam. For example, according to a firstreception beam configuration 2 e-20, four downlink reception beams areused to cover all directions, the internal angle 2 e-10 of a beam is 90degrees, and a width/coverage is as shown in the diagram 2 e-15.According to a second reception beam configuration 2 e-35, 8 downlinkreception beams are used to cover all directions, the internal angle 2e-25 of a beam is 45 degrees, and a width/coverage is as shown in thediagram 2 e-30, unlike the first reception beam configuration 2 e-20.

In other words, according to the first reception beam configuration 2e-20, in order to determine an optimal reception beam for a singletransmission beam, the corresponding transmission beam needs to bereceived four times (i.e., a reception beam sweeping length is 4).According to the second reception beam configuration 2 e-35, in order todetermine an optimal reception beam for a single transmission beam, thecorresponding transmission beam needs to be received 8 times (i.e., areception beam sweeping length is 8). FIGS. 2B and 2E describe a beam indifferent formats, but both are examples for describing a beam.

FIG. 2F is a diagram illustrating the operation of a UE according to anembodiment of the present disclosure.

Referring to FIG. 2F, in operation 2 f-05, an idle-state UE applies afirst reception beam configuration and receives a first downlink signal.The first reception beam configuration may be reference configurationinformation, and may be information associated with a common downlinkreception beam.

The first downlink signal is a beam reference signal received in apreconfigured first subframe, and the first subframe may be an OSFtransmitted from a TRP.

The first downlink signal is repeatedly transmitted at regularintervals. Accordingly, receiving the first downlink signal by applyingthe first reception beam configuration indicates that a measurementperiod that is proportional to the number of reception beams (or areception beam sweeping length) of the first reception beamconfiguration is used in order to determine an optimal reception beamfor the single first downlink signal or in order to determine thereceived quality of the first downlink signal. For example, if the beamsweeping length of the first reception beam configuration is 4, or ifthe internal angle/width of a beam is 90 degrees, the measurement periodneeded to determine the received quality of a single transmission beamis 4 units of time.

The first reception beam configuration is determined on the basis of afirst parameter and a second parameter, wherein the first parameter isdetermined for each frequency band or is indicated by systeminformation, and the second parameter is determined by the capability ofa UE. The first parameter and the second parameter may be parameters forspecifying the width of a reception beam, parameters for specifying theangle (or internal angle) of a reception beam, or parameters forspecifying the number of reception beams (or a reception beam sweepinglength) needed to cover all directions. If the first parameter and thesecond parameter are used for specifying the angle of a reception beam,the first reception beam configuration may be determined to be thelarger value between the first parameter and the second parameter. Ifthe first parameter and the second parameter are used for specifying thewidth of a reception beam or the number of reception beams, the firstreception beam configuration may be determined to be the smaller valuebetween the first parameter and the second parameter.

In operation 2 f-10, the UE may receive a signal by applying the firstreception beam configuration. The UE may apply the first reception beamconfiguration, and may receive a paging message in a serving downlinktransmission beam.

In operation 2 f-15, it is determined whether the UE needs to set up anRRC connection. If it is determined that the UE needs to set up an RRCconnection, a higher-layer device of the UE directs an access-layerdevice of the UE to set up an RRC connection. Subsequently, the UEproceeds with operation 2 f-20.

In operation 2 f-20, the UE performs a random access procedure. The UEperforms a random access procedure with a TRP by applying the firstreception beam configuration.

In operation 2 f-25, the UE initiates a reception beam refinementprocedure with the TRP according to an indication by a base station.When the reception beam refinement procedure is initiated, the UEchanges to a second reception beam configuration, and determines anoptimal reception beam of the second reception beam configuration viathe reception beam refinement procedure.

The second reception beam configuration is determined on the basis of afirst parameter and a second parameter, determined on the basis of thecapability of the UE, or may be determined on the basis of a thirdparameter. If the first parameter and the second parameter are used forspecifying the angle of a reception beam, the second reception beamconfiguration may be determined to be the smaller value between thefirst parameter and the second parameter. If the first parameter and thesecond parameter are used for specifying the width of a reception beamor the number of reception beams, the second reception beamconfiguration may be determined to be a higher value between the firstparameter and the second parameter. Alternatively, the second receptionbeam configuration may be determined on the basis of the thirdparameter, and the third parameter may be a value inferred based on aparameter transmitted by a CU or a TRP. For example, if the thirdparameter is defined to be the maximum time (i.e., a measurement periodfor a downlink beam) spent when a UE determines an optimal receptionbeam for a preconfigured beam or a UE completes measurement of thepreconfigured beam, the UE may set the number of reception beams or theinternal angle of a reception beam such that the measurement period issatisfied and the best reception performance is obtained.

In operation 2 f-30, the UE may apply the second reception beamconfiguration, and may receive a second downlink reception signal usinga reception beam. The second downlink reception signal may betransmitted in a second subframe, and may be a reference signal used forestimating a channel status, or may be user data transmitted to the UE.The second subframe may be a data subframe (DSF).

FIG. 2G is a diagram of the structure of a UE according to an embodimentof the present disclosure.

Referring to FIG. 2G, the UE may include a radio-frequency (RF)processor 2 g-10, a baseband processor 2 g-20, a storage unit 2 g-30,and a controller 2 g-40.

The RF processor 2 g-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 2 g-10 up-convertsa baseband signal provided from the baseband processor 2 g-20 into an RFband signal, transmits the RF band signal via an antenna, anddown-converts the RF band signal received via the antenna into abaseband signal. For example, the RF processor 2 f-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. Although only a single antenna isillustrated in the drawing, the UE may include a plurality of antennas.In addition, the RF processor 2 g-10 may include a plurality of RFchains. In addition, the RF processor 2 g-10 may perform beamforming.For the beamforming, the RF processor 2 g-10 may control the phase andthe size of each signal transmitted/received via a plurality of antennasor antenna elements. Also, the RF processor may perform MIMO, and mayreceive a plurality of layers while performing MIMO operation. The RFprocessor 2 g-10 may appropriately configure a plurality of antennas orantenna elements according to the control of the controller so as toperform reception beam sweeping, or may control the orientation of areception beam and a beam width such that a reception beam accords witha transmission beam.

The baseband processor 2 g-20 performs a function for conversion betweena baseband signal and a bitstream according to the physical layerstandard of the system. For example, in the case of data transmission,the baseband processor 2 g-20 generates complex symbols by encoding andmodulating a transmission bitstream. Further, in the case of datareception, the baseband processor 2 g-20 reconstructs a receptionbitstream by demodulating and decoding a baseband signal provided fromthe RF processor 2 g-10. For example, according to anorthogonal-frequency-division-multiplexing (OFDM) scheme, in the case ofdata transmission, the baseband processor 2 g-20 generates complexsymbols by encoding and modulating a transmission bitstream, maps thecomplex symbols to subcarriers, and then configures OFDM symbols via anIFFT (inverse fast Fourier transform) operation and a CP (cyclic prefix)insertion. Further, in the case of data reception, the basebandprocessor 2 g-20 divides the baseband signal provided from the RFprocessor 2 g-10 into OFDM symbol units, reconstructs the signals mappedto the subcarriers via a fast Fourier transform (FFT) operation, andthen reconstructs a reception bitstream via demodulation and decoding.

The baseband processor 2 g-20 and the RF processor 2 g-10 transmit andreceive a signal, as described above. Accordingly, each of the basebandprocessor 2 g-20 and the RF processor 2 g-10 may be referred to as atransmitter, a receiver, a transceiver, or a communication unit. Inaddition, at least one of the baseband processor 2 g-20 or the RFprocessor 2 g-10 may include a plurality of communication modules so asto support many different radio access technologies. In addition, atleast one of the baseband processor 2 g-20 or the RF processor 2 g-10may include different communication modules to process signals ofdifferent frequency bands. For example, the different radio accesstechnologies may include an LTE network, an NR network, and the like.Further, the different frequency bands may include a super-highfrequency (SHF) (e.g., 2.5 GHz and 5 GHz) band and a millimeter (mm)wave (e.g., 60 GHz) band.

The storage unit 2 g-30 stores data such as a basic program, anapplication program, and configuration information for the operation ofthe UE. The storage unit 2 g-30 may provide stored data in response to arequest from the controller 2 g-40.

The controller 2 g-40 controls the overall operation of the UE. Forexample, the controller 2 g-40 transmits and receives a signal via thebaseband processor 2 g-20 and the RF processor 2 g-10. Also, thecontroller 2 g-40 writes and reads data to/from the storage unit 2 g-40.To this end, the controller 2 g-40 may include at least one processor.For example, the controller 2 g-40 may include a communication processor(CP), which performs control for communication, and an applicationprocessor (AP), which controls a higher layer such as an applicationprogram. The controller 2 g-40 may include a multiple-access processor 2g-42. Also, the controller 2 g-40 may control the operations of the UEaccording to the second embodiment of the present disclosure. Thecontroller 2 g-40 may control the operations of the UE, which have beendescribed with reference to FIGS. 2A to 2F.

FIG. 2H is a block diagram of a TRP in a wireless communication systemaccording to an embodiment of the present disclosure. A base station mayinclude at least one TRP.

Referring to FIG. 2H, the base station may include an RF processor 2h-10, a baseband processor 2 h-20, a backhaul communication unit 2 h-30,a storage unit 2 h-40, and a controller 2 h-50.

The RF processor 2 h-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 2 h-10 up-convertsa baseband signal provided from the baseband processor 2 h-20 into an RFband signal and then transmits the converted signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal. For example, the RF processor 2 h-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although only a single antenna is illustrated in thedrawing, a first access node may include a plurality of antennas. Inaddition, the RF processor 2 h-10 may include a plurality of RF chains.In addition, the RF processor 2 h-10 may perform beamforming. For thebeamforming, the RF processor 2 h-10 may control the phase and the sizeof each of the signals transmitted and received via a plurality ofantennas or antenna elements. The RF processor may perform downlink MIMOoperation by transmitting one or more layers.

The baseband processor 2 h-20 performs a function of converting betweena baseband signal and a bitstream according to the physical layerstandard of a first radio access technology. For example, in the case ofdata transmission, the baseband processor 2 h-20 generates complexsymbols by encoding and modulating a transmission bitstream. Further, inthe case of data reception, the baseband processor 2 h-20 reconstructs areception bitstream by demodulating and decoding a baseband signalprovided from the RF processor 2 h-10. For example, according to an OFDMscheme, in the case of data transmission, the baseband processor 2 h-20generates complex symbols by encoding and modulating the transmissionbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols via an IFFT operation and CP insertion. Also, in the caseof data reception, the baseband processor 2 h-20 divides a basebandsignal provided from the RF processor 2 h-10 into OFDM symbol units,restores signals mapped onto the subcarriers via the FFT operation, andrestores a reception bitstream via demodulation and decoding. Thebaseband processor 2 h-20 and the RF processor 2 h-10 transmit andreceive a signal as described above. Accordingly, each of the basebandprocessor 2 h-20 and the RF processor 2 h-10 may be referred to as atransmitter, a receiver, a transceiver, a communication unit, or awireless communication unit.

The communication unit 2 h-30 provides an interface for performingcommunication with other nodes in a network. The communication unit 2h-30 may be referred to as “backhaul communication unit”.

The storage unit 2 h-40 may store data, such as a basic program, anapplication program, configuration information, or the like, used foroperating the main base station. Particularly, the storage unit 2 h-40may store information associated with a bearer allocated to a connectedUE, a measurement result reported from a connected UE, and the like.Also, the storage unit 2 h-40 may store information which is a criterionto determine whether to provide or interrupt multiple access to a UE.The storage unit 2 h-40 may provide stored data in response to a requestfrom the controller 2 h-50.

The controller 2 h-50 may control the overall operation of the main basestation. For example, the controller 2 h-50 may transmit and receive asignal via the baseband processor 2 h-20 and the RF processor 2 h-10 orthe backhaul communication unit 2 h-30. Also, the controller 2 h-50writes and reads data to/from the storage unit 2 h-40. To this end, thecontroller 2 h-50 may include at least one processor. The controller 2h-50 may include a multiple-access processor 2 h-52. Also, thecontroller 2 h-50 may control the operation of the base station or TRPaccording to the second embodiment of the present disclosure. Thecontroller 2 h-50 may control the operations of the base station or TRPwhich have been described with reference to FIGS. 2A to 2F.

Third Embodiment

The present disclosure relates to serving beam reselection of a UE in anext-generation mobile communication system that operates on the basisof a beam, and relates to a method and apparatus for applying a gradualreselection criterion on the basis of the type of a neighboring cell.

The recent mobile communication system is being developed by graftingvarious new technologies in order to satisfy various demands forservices and increasing data traffic. Particularly, the discussion onthe 5^(th) generation (5G), which is a next-generation mobilecommunication system that takes into consideration the demands, has beenactively conducted. The 5G system is referred to as a new radio accesstechnology (hereinafter NR). The NR system aims to provide asuper-high-speed data service of several Gbps by using an ultra-widebandgreater than 100 MHz, unlike the legacy LTE and LTE-A. However, it isdifficult to secure an ultra-wideband frequency greater than 100 MHz ina frequency band of hundreds of MHz or several GHz used in LTE andLTE-A. The NR system considers a method of transmitting a signal using awide frequency band existing in a frequency band greater than 6 GHz.Particularly, the NR system considers a method of increasing atransmission rate by using a millimeter wave (hereinafter, mmWave) bandsuch as a 28 GHz band, a 60 GHz band, or the like. Since a frequencyband and the path loss of a radio wave are proportional to each other,the path loss of a radio wave is high in super-high frequencies, and aservice area is small. In the NR system, a beamforming technology, whichgenerates a directional beam using a plurality of antennas so as toincrease a travel distance of a radio wave, is emphasized as animportant technology in order to overcome the drawback of a smallservice area. The beamforming technology may be applied to each of atransmission end and a reception end, and the beamforming technology mayincrease a service area, and may decrease interference attributable tophysical beam concentration in a target direction. Also, in the case ofdirectional-beam-based transmission, transmission or reception of asignal may be difficult at a location where a beam is not formed. Inorder to overcome the above-described drawback, beam sweeping is used.Beam sweeping is a scheme in which a transmission apparatus sequentiallysweeps and rotates, and transmits directional beams having apreconfigured beam width, such that a beam is received by a receptionapparatus which exists within a beam range of the transmissionapparatus.

FIG. 3A is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 3A, a cell serviced by an NR node B (NR NB or a basestation) 3 a-05 that operates on the basis of a beam may include varioustransmission reception points (TRPs) 3 a-10, 3 a-15, 3 a-20, 3 a-25, 3a-30, 3 a-35, and 3 a-40. The TRPs 3 a-10 to 3 a-40 are blocks which areseparated from a legacy LTE eNB so as to perform only a function oftransmitting and receiving a physical signal, and include a plurality ofantennas. Particularly, the TRPs 3 a-10 to 3 a-40 may generate beams invarious directions using a plurality of transmission and receptionantennas, and may perform beamforming, and may be referred to as a beamgroup (BG). A UE 3 a-50 may access an NR NB 3 a-05 or an externalnetwork via the TRPs 3 a-10 to 3 a-40. The NR NB 3 a-05 may performscheduling by collecting status information such as the buffer status ofUEs, an available transmission power status, a channel status, or thelike, and may support connection between the UEs and a core network(CN), so as to service traffic of users. The NR NB 3 a-05 may notinclude a TRP. In this instance, a scenario of directly performingcommunication with UEs 3 a-50 within the cell using different beams maybe taken into consideration.

Also, in the NR system, an MME may be a device that takes charge invarious control functions as well as a mobility management functionassociated with the UE 3 a-50, and is connected to a plurality of NR NBs3 a-05, and an S-GW is a device that provides a data bearer. Also, theMME and the S-GW 3 a-45 may further perform authentication for the UE 3a-50 that accesses a network, bearer management, and the like, and mayprocess a packet received from the NR NB 3 a-05 or a packet to betransmitted to the NR NB 3 a-05.

FIG. 3B is a diagram illustrating the structure of a frame used by an NRsystem that operates on the basis of a beam according to an embodimentof the present disclosure.

Referring to FIG. 3B, a radio frame 3 b-05 of the NR system includes aplurality of subframes 3 b-10. Particularly, the subframe of the NRsystem may include two types, namely an overhead subframe (OSF) 3 b-15and a data subframe (DSF) 3 b-20.

The overhead subframe 3 b-15 is a subframe in which a common overheadsignal required for beam selection is transmitted, and a differentoverhead signal is transmitted according to a beam sweeping scheme foreach symbol included in the subframe. The overhead subframe 3 b-15 mayinclude a primary synchronization signal (PSS) for obtaining a timing ofan orthogonal-frequency-division-multiplexing (OFDM) symbol, a secondarysynchronization signal (SSS) for detecting a cell ID, an extendedsynchronization signal (ESS) for obtaining a timing of a subframe, and abeam reference signal (BRS) for identifying a beam. Also, a physicalbroadcast channel (PBCH) may be transmitted, and may include systeminformation, a master information block (MIB), or essential informationfor a UE to access a system (e.g., including a downlink beam bandwidth,a system frame number or the like). Single or multiple overheadsubframes 3 b-15 may exist in a radio frame 3 b-05. In the presentdiagram, transmission occurs in a 0^(th) radio frame and 25^(th) radioframe.

The data subframe 3 b-20 is a subframe in which data is actuallytransmitted to a preconfigured UE, and a different beam pattern may beapplied depending on the geographical distribution of UEs. A TRP 3 b-25performs beam sweeping in a different direction for each symbol duringthe overhead subframe 3 b-15. On the basis of the result of measurementbased thereon, resources for data transmission and reception with UEsmay be allocated for each beam 3 b-30, 3 b-35, and 3 b-40 in the datasubframe 3 b-20. If the orientation of a beam transmitted by the TRP 3b-25 does not match the position of a UE, the UE may not receive anysignal in the corresponding data subframe. Also, a single TRP 3 b-25 maytransmit many data subframes during a single radio frame 3 b-05, and mayreceive many beams from many TRPs 3 b-25 depending on the position ofthe UE.

FIG. 3C is a diagram illustrating the procedure in which a UE reselectsa cell in an LTE system according to an embodiment of the presentdisclosure.

The cell reselection is a procedure to determine the cell on which theUE is to camp when the service quality of a serving cell is lower thanthe service quality of a neighboring cell due to the movement of anidle-state UE or a change of a channel status. Handover is determined onthe basis of a network (an MME or a source eNB). However, cellreselection is determined by a UE on the basis of a measurement value.Also, a cell that is reselected as a UE moves may be a cell that usesthe same LTE frequency as that of the serving cell on which the UEcurrently camps, a cell that uses a different LTE frequency(inter-frequency), or a cell that uses a different radio accesstechnology. The cell that uses the same frequency as that of the currentserving cell is referred to as an intra frequency cell. The cell thatuses a frequency different from that of the serving cell is referred toas an inter-frequency cell.

In operation 3 c-05, it is assumed that an idle-state UE camps on aserving cell. The idle-state UE camps on the serving cell and performs aseries of operations.

In operation 3 c-10, the UE obtains a system information block (SIB).The UE receives system information broadcasted by a base station of theserving cell. In the system information, MIB, SIB 1, and SIB2 are systeminformation applied in common to all UEs. SIB3 to SIB8 includeinformation needed when an idle-state UE reselects a cell. The systeminformation may include a threshold value used to determine whether tomeasure a neighboring cell signal, a parameter used when calculating theranks of a serving cell and neighboring cells, and the like.

In operation 3 c-15, the UE measures a signal of the serving cell. Theidle-state UE may wake up at discontinuous reception (DRX) intervals soas to measure an absolute signal strength (a reference signal receivedpower (RSRP)Q_(rxlevmeas)) and a relative signal quality (a referencesignal received quality (RSRQ) Q_(qualmeas)) of the serving cell. Usingthe measurement values and the parameters received from the basestation, the UE may calculate the received level (Srxlev) and thereceived quality (Squal) of the serving cell and may compare the valueswith threshold values so as to determine whether to perform cellreselection. The received level (Srxlev) and the received quality(Squal) of the serving cell are calculated according to the equationbelow.Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q_(rxlevminoffset))−Pcompensation−Qoffset_(temp)Squal=Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset))−Qoffset_(temp)

For the definitions of the parameters used herein, refer to the 3GPPstandard document “36.304: User Equipment (UE) procedures in idle mode”.

In operation 3 c-20, the UE may determine whether a cell reselectionoperation is triggered. The UE may determine whether to trigger a cellreselection operation on the basis of the measurement values. If thestrength and the quality of a signal of the serving cell calculated fromthe measurement values is lower than a threshold value(Srxlev<SIntraSearchP or Squal<SIntraSearchQ), it is identified that atrigger condition for cell reselection is satisfied, and the cellreselection operation is triggered. When the condition is not satisfied,the UE may not trigger the cell reselection operation. If the cellreselection operation is not triggered, the UE proceeds with operation 3c-25, and the UE may continuously camp on the corresponding serving cellwithout cell reselection.

If the condition is satisfied and cell reselection is triggered, the UEproceeds with operation 3 c-30. The UE measures neighboring cells on thebasis of priority. With respect to an inter-frequency/inter-RAT cellhaving a high priority, the UE initiates neighboring cell measurementirrespective of the quality of the serving cell. Also, with respect toan inter-frequency cell having the same or lower priority than that ofthe serving cell, the UE may initiate neighboring cell measurement ifthe strength and the quality of a signal of the serving cell are lowerthan threshold values (SnonIntraSearchP, SnonIntraSearchQ) received viathe system information, that is, if Srxlev<SnonIntraSearchP orSqual<SnonIntraSearchQ is satisfied.

When the measurement of neighboring cells is completed, the UE performscell reselection on the basis of priority in operation 3 c-35. First, inassociation with reselection of an inter-frequency/inter-RAT cell havinga high priority, if the signal quality of the corresponding cell isgreater than a threshold value ThreshX, HighQ during a preconfiguredperiod of time TreselectionRAT (Squal>ThreshX, HighQ), the UE reselectsthe corresponding cell. Second, in association with reselection of aninter-frequency cell having a low priority, the UE determines whetherthe condition that the signal quality of the serving cell is lower thana threshold value ThreshServing, LowQ (Squal<ThreshServing, LowQ) issatisfied, and if the condition is satisfied and the signal quality ofthe inter-frequency cell is greater than a threshold value ThreshX, LowQduring a preconfigured period of time TreselectionRAT (Squal>ThreshX,LowQ), the UE reselects the corresponding cell in operation 3 c-40.Third, in association with reselection of anintra-frequency/inter-frequency cell having the same priority, the UEcalculates a rank for each cell on the basis of the measurement values(e.g., RSRP) associated with neighboring cells. Ranks of a serving celland a neighboring cell are calculated, respectively, as below.Rs=Q _(meas,s) +Q _(Hyst) −Qoffset_(temp)Rn=Q _(meas,n) −Qoffset−Qoffset_(temp)

Here, Q_(meas,s) denotes the RSRP measurement value of a serving cell.Q_(meas,n) denotes the RSRP measurement value of a neighboring cell.Q_(Hyst) denotes the hysteresis value of a serving cell. Qoffset denotesan offset value between a serving cell and a neighboring cell.Qoffset_(temp) denotes an offset temporarily applied to a cell. If therank of a neighboring cell calculated from the above equation is higherthan the rank of the serving cell (Rn>Rs), the UE camps on an optimalcell among the neighboring cells.

If reselection is determined in the above-described process, the UEreceives system information from the corresponding cell and checkssuitability, that is, whether the UE is serviced via the new servingcell, in operation 3 c-40. If a tracking area identity (TAI) is notincluded in a TAI list of the UE, the UE proceeds with a tracking areaupdate (TAU) procedure, and if the corresponding cell is determined tobe a new cell, the cell performs operations of a serving cell (obtainingsystem information, paging monitoring, serving cell signal measurement).

FIG. 3D is a diagram illustrating a method in which a UE reselects aserving beam in an NR system according to an embodiment of the presentdisclosure.

In operation 3 d-05, an idle-state NR UE camps on an n^(th) beam of aserving TRP. In operation 3 d-10, the UE monitors a paging message. Inoperation 3 d-15, the UE receives system information via a serving beam.In operation 3 d-20, the UE measures the serving beam and neighboringbeams.

If the result of measurement of neighboring beams corresponds to a beamreselection condition, the UE reselects a beam in operation 3 d-25.Hereinafter, beam reselection in an NR system proposed in the presentdisclosure will be described in detail.

FIG. 3E is a diagram illustrating a beam reselection method of an NRsystem according to an embodiment of the present disclosure.

In operation 3 e-05, a UE 3 e-01 camps on a beam 3 e-02 of a TRP/BG.

In operation 3 e-10, the UE 3 e-01 monitors a paging message.

In operation 3 e-15, the UE 3 e-01 measures the strength and the qualityof a downlink beam reference signal of the serving beam. The downlinkbeam reference signal is transmitted and received via an overheadsubframe of the corresponding TRP/BG.

In operation 3 e-20, the UE 3 e-01 measures the strength and the qualityof the downlink reference signal of the serving beam with apreconfigured reference value. On the basis of the comparison result,the UE may determine whether to measure neighboring beams. If thestrength and the quality of the downlink signal of the serving beam arelower than preconfigured threshold values (received via systeminformation), the UE 3 e-01 may measure neighboring beams in operation 3e-25. The measurement values may include measurements of neighboringbeams included in an intra-TRP, an inter-TRP, and an inter-frequencycell.

In operation 3 e-30, the UE 3 e-01 calculates a ranking reference value.The UE 3 e-01 may calculate the ranking reference value on the basis ofthe signal strength of the serving beam and the measurement value of aneighboring beam. The equation used for calculating the rankingreference value is as given below.Rs=Q _(meas,s) +Q _(Hyst)Rn=Q _(meas,n) −Qoffset_BG

Here, Q_(meas,s) denotes the RSRP measurement value of a serving beam.Q_(meas,n) denotes the RSRP measurement value of a neighboring beam.Q_(Hyst) denotes the hysteresis value of a serving beam, and Qoffset_BGdenotes an offset between a serving beam and a neighboring beam group,and includes a first offset and a second offset. Also, a firstneighboring beam (intra-TRP neighboring beam) is defined to be aneighboring beam included in the beam group to which the serving beambelongs. A second neighboring beam (inter-TRP neighboring beam) isdefined to be a neighboring beam included in a beam group that isdifferent from the beam group to which the serving beam belongs. Thefirst offset is applied when the ranking reference value of the firstneighboring beam is calculated. The second offset is applied when theranking reference value of the second neighboring beam is calculated. Ifthe ranking value of the neighboring beam, calculated from the aboveequation, is higher than the ranking value of the serving beam (Rn>Rs),the UE camps on an optimal beam among the neighboring beams. The beamreselection of the present embodiment will be described below in detail.

In operation 3 e-35, the UE 3 e-01 identifies the neighboring beam groupthat the highest-ranking beam belongs to. If the highest-ranking beam isthe first neighboring beam (intra-TRP neighboring beam), the UEdetermines whether a first condition is satisfied. If the firstcondition is satisfied, the UE performs beam reselection in operation 3e-45. The UE 3 e-01 may perform beam reselection operation with respectto the first neighboring beam.

In operation 3 e-45, the UE 3 e-01 identifies whether a neighboring beamgroup that the highest-ranking beam belongs to. If the highest-rankingbeam is a second neighboring beam (inter-TRP neighboring beam), the UEdetermines whether a second condition is satisfied. If the secondcondition is satisfied, the UE performs beam reselection in operation 3e-50. The UE 3 e-01 may perform beam reselection operation with respectto the second neighboring beam.

Here, the first condition is satisfied when a corresponding beam isranked higher than the serving beam during a period 1-1 and a period 1-2elapses after a serving beam is reselected. The second condition issatisfied when a corresponding beam is ranked higher than the servingbeam during a period 2-1 and a period 2-2 elapses after a serving beamis reselected. That is, in the embodiment of the present disclosure, acondition may be applied differently on the basis of the group to whichthe highest-ranking beam belongs. Different conditions may beinformation associated with the period 1-1, the period 1-2, the period2-1, and the period 2-2, as described above.

The first offset, the second offset, the period 1-1, and the period 2-1described above may be provided via the system information. Also, theperiod 1-2 and the period 2-2 may be provided via the systeminformation, or may be determined in advance. That is, in the embodimentof the present disclosure, TreselectionRAT, which is used for cellreselection in LTE, is classified gradually as the period 1-1 and theperiod 2-1 on the basis of the neighboring beam group to which thehighest-ranking beam belongs, and minimum ToS (Time of Stay), which isused to prevent repetitive cell reselection, is gradually defined to bethe period 1-2 and the period 2-2, which are used for the cellreselection operation.

FIG. 3F is a diagram illustrating operations of a UE when the UEreselects a serving beam in an NR system according to the firstembodiment of the present disclosure. The UE may operate as follows. Forthe detailed operation of the UE in FIG. 3F, refer to the correspondingoperations in FIG. 3E.

The UE camps on a beam of a TRP/BG in operation 3 f-05, and the UEmonitors a paging message in operation 3 f-10.

In operation 3 f-15, the UE obtains system information. In operation 3f-20, the UE may measure the strength and quality of a downlink beamreference signal of a serving beam. Here, the downlink beam referencesignal is transmitted and received in an overhead subframe of acorresponding beam.

In operation 3 f-25, the UE may compare the strength and quality of thedownlink reference signal of the serving beam with a preconfiguredreference value.

In operation 3 f-30, the UE measures neighboring beams. The UE initiatesmeasurement of neighboring beams if the downlink reference signalstrength is lower than a reference value or the downlink signal qualityis lower than a reference value.

In operation 3 f-35, the UE calculates a ranking reference value. The UEcalculates the ranking reference value on the basis of the measuredsignal strength of a neighboring beam and the signal strength of theserving beam.

The equation used for calculating the ranking reference value is asgiven below.Rs=Q _(meas,s) +Q _(Hyst)Rn=Q _(meas,n) −Qoffset_BG

Q_(meas,s) denotes the RSRP measurement value of a serving beam.Q_(meas,n) denotes the RSRP measurement value of a neighboring beam.Q_(Hyst) denotes the hysteresis value of a serving beam, and Qoffset_BGdenotes an offset between a serving beam and a neighboring beam group,and includes a first offset and a second offset. Here, a firstneighboring beam (intra-TRP neighboring beam) is defined to be aneighboring beam included in the beam group to which the serving beambelongs. A second neighboring beam (inter-TRP neighboring beam) isdefined to be a neighboring beam included in a beam group that isdifferent from the beam group to which the serving beam belongs. Thefirst offset is applied when the ranking reference value of the firstneighboring beam is calculated. The second offset is applied when theranking reference value of the second neighboring beam is calculated.

If the serving beam is the highest-ranking beam, the current servingbeam is maintained.

In operation 3 f-40, if a neighboring beam is the highest-ranking beam,the UE determines whether the highest-ranking beam is the firstneighboring beam or the second neighboring beam. If the highest-rankingbeam is the first neighboring beam, the UE may perform beam reselectionby taking into consideration whether a first condition is satisfied. Ifthe highest-ranking beam is the second neighboring beam, the UE mayperform beam reselection by taking into consideration whether a secondcondition is satisfied.

The first condition is satisfied when a corresponding beam is rankedhigher than the serving beam during a period 1-1 and a period 1-2elapses after a serving beam is reselected. That is, the UE may performcontrol such that the corresponding beam is ranked higher than theserving beam during the period 1-1, and the reselected beam ismaintained during the period 1-2.

The second condition is satisfied when a corresponding beam is rankedhigher than the serving beam during a period 2-1 and a period 2-2elapses after a serving beam is reselected. That is, the UE may performcontrol such that the corresponding beam is ranked higher than theserving beam during the period 1-2, and the reselected beam ismaintained during the period 2-2.

The first offset, the second offset, the period 1-1, and the period 2-1may be provided via system information. Also, the period 1-2 and theperiod 2-2 may be provided via the system information, or may bedetermined in advance.

FIG. 3G is a block diagram of a UE according to an embodiment of thepresent disclosure.

Referring to FIG. 3G, the UE according to an embodiment of the presentdisclosure may include a radio-frequency (RF) processor 3 g-10, abaseband processor 3 g-20, a storage unit 3 g-30, and a controller 3g-40.

The RF processor 3 g-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 3 g-10 up-convertsa baseband signal provided from the baseband processor 3 g-20 into an RFband signal, transmits the RF band signal via an antenna, anddown-converts the RF band signal, received via the antenna, into abaseband signal. For example, the RF processor 3 g-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. Although only a single antenna isillustrated in the drawing, the UE may include a plurality of antennas.In addition, the RF processor 3 g-10 may include a plurality of RFchains. Moreover, the RF processor 3 g-10 may perform beamforming. Forthe beamforming, the RF processor 3 g-10 may control the phase and thesize of each signal transmitted/received via a plurality of antennas orantenna elements. Also, the RF processor 3 g-10 may perform MIMO, andmay receive a plurality of layers while performing a MIMO operation. TheRF processor 3 g-10 may appropriately configure a plurality of antennasor antenna elements according to the control of the controller 3 g-40,so as to perform reception beam sweeping, or may control the orientationof a reception beam and a beam width such that a reception beam accordswith a transmission beam.

The baseband processor 3 g-20 executes a function of converting betweena baseband signal and a bitstream on the basis of the physical layerstandard of a system. For example, in the case of data transmission, thebaseband processor 3 g-20 generates complex symbols by encoding andmodulating a transmission bitstream. In addition, in the case of datareception, the baseband processor 3 g-20 recovers a reception bitstreamvia the demodulation and decoding of a baseband signal provided from theRF processor 3 g-10. For example, according to an OFDM scheme, in thecase of data transmission, the baseband processor 3 g-20 generatescomplex symbols by encoding and modulating a transmission bitstream,maps the complex symbols to subcarriers, and then configures OFDMsymbols via an inverse fast Fourier transform (IFFT) operation and acyclic prefix (CP) insertion. Further, in the case of data reception,the baseband processor 3 g-20 divides the baseband signal provided fromthe RF processor 3 g-10 into OFDM symbol units, reconstructs the signalsmapped to the subcarriers via a fast Fourier transform (FFT) operation,and then reconstructs the reception bitstream via demodulation anddecoding.

The baseband processor 3 g-20 and the RF processor 3 g-10 transmit andreceive a signal as described above. Accordingly, each of the basebandprocessor 3 g-20 and the RF processor 3 g-10 may be referred to as atransmitter, a receiver, a transceiver, or a communication unit. Inaddition, at least one of the baseband processor 3 g-20 or the RFprocessor 3 g-10 may include a plurality of communication modules so asto support many different radio access technologies. In addition, atleast one of the baseband processor 3 g-20 or the RF processor 3 g-10may include different communication modules so as to process signals ofdifferent frequency bands. For example, the different radio accesstechnologies may include an LTE network, an NR network, and the like.Further, the different frequency bands may include a super-highfrequency (SHF) (e.g., 2.5 GHz and 5 GHz) band and a millimeter (mm)wave (e.g., 60 GHz) band.

The storage unit 3 g-30 stores data such as a basic program, anapplication program, and configuration information for the operation ofthe UE. The storage unit 3 g-30 may provide stored data in response to arequest from the controller 3 g-40.

The controller 3 g-40 controls the overall operation of the UE. Forexample, the controller 3 g-40 transmits and receives a signal via thebaseband processor 3 g-20 and the RF processor 3 g-10. Also, thecontroller 3 g-40 writes and reads data to/from the storage unit 3 g-40.To this end, the controller 3 g-40 may include at least one processor.For example, the controller 3 g-40 may include a communication processor(CP), which performs control for communication, and an applicationprocessor (AP), which controls a higher layer such as an applicationprogram. The controller 3 g-40 may include a multiple-access processor 3g-42. Also, the controller 3 g-40 may control the operations of the UEaccording to the third embodiment of the present disclosure. Thecontroller 3 g-40 may control the operations of the UE which have beendescribed with reference to FIGS. 3A to 3F.

FIG. 3H is a block diagram of a TRP in a wireless communication systemaccording to an embodiment of the present disclosure. A base station mayinclude at least one TRP.

Referring to FIG. 3H, the base station according to an embodiment of thepresent disclosure may include an RF processor 3 h-10, a basebandprocessor 3 h-20, a backhaul communication unit 3 h-30, a storage unit 3h-40, and a controller 3 h-50.

The RF processor 3 h-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 3 h-10 up-convertsa baseband signal provided from the baseband processor 3 h-20 into an RFband signal and then transmits the converted signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal. For example, the RF processor 3 h-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although only a single antenna is illustrated in thedrawing, a first access node may include a plurality of antennas. Inaddition, the RF processor 3 h-10 may include a plurality of RF chains.Moreover, the RF processor 3 h-10 may perform beamforming. For thebeamforming, the RF processor 3 h-10 may control the phase and the sizeof each of the signals transmitted and received via a plurality ofantennas or antenna elements. The RF processor may perform downlink MIMOoperation by transmitting one or more layers.

The baseband processor 3 h-20 performs a function of converting betweena baseband signal and a bitstream according to the physical layerstandard of a first radio access technology. For example, in the case ofdata transmission, the baseband processor 3 h-20 generates complexsymbols by encoding and modulating a transmission bitstream. Further, inthe case of data reception, the baseband processor 3 h-20 reconstructs areception bitstream by demodulating and decoding a baseband signalprovided from the RF processor 3 h-10. For example, according to an OFDMscheme, in the case of data transmission, the baseband processor 3 h-20generates complex symbols by encoding and modulating a transmissionbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols via an IFFT operation and CP insertion. Also, in the caseof data reception, the baseband processor 3 h-20 divides a basebandsignal provided from the RF processor 3 h-10 into OFDM symbol units,restores signals mapped onto the subcarriers via the FFT operation, andrestores a reception bitstream via demodulation and decoding. Thebaseband processor 3 h-20 and the RF processor 3 h-10 transmit andreceive a signal as described above. Accordingly, each of the basebandprocessor 3 h-20 and the RF processor 3 h-10 may be referred to as atransmitter, a receiver, a transceiver, a communication unit, or awireless communication unit.

The communication unit 3 h-30 provides an interface for performingcommunication with other nodes in a network. The communication unit 3h-30 may be referred to as a “backhaul communication unit”.

The storage unit 3 h-40 may store data, such as a basic program, anapplication program, configuration information, or the like, used foroperating the main base station. Particularly, the storage unit 3 h-40may store information associated with a bearer allocated to a connectedUE, a measurement result reported from a connected UE, and the like.Also, the storage unit 3 h-40 may store information which is a criterionto determine whether to provide or interrupt multiple access to a UE.The storage unit 3 h-40 may provide stored data in response to a requestfrom the controller 3 h-50.

The controller 3 h-50 may control the overall operation of the main basestation. For example, the controller 3 h-50 may transmit and receive asignal via the baseband processor 3 h-20 and the RF processor 3 h-10 orthe backhaul communication unit 3 h-30. Also, the controller 3 h-50writes and reads data to/from the storage unit 3 h-40. To this end, thecontroller 3 h-50 may include at least one processor. The controller 3h-50 may include a multiple-access processor 3 h-52. Also, thecontroller 3 h-50 may control the operations of the base station or TRPaccording to the third embodiment of the present disclosure. Thecontroller 3 h-50 may control the operations of the base station or TRP,which have been described with reference to FIGS. 3A to 3F.

Fourth Embodiment

An embodiment of the present disclosure relates to a method and anapparatus for performing a HARQ operation differently based on whetherconditional transmission is set for decreasing a delay or on whetherconditional transmission is not set.

In the present disclosure, a UE selectively applies an unconditionaltransmission operation or a conditional transmission operation accordingto an indication by a base station, and particularly, an HARQ operationis applied differently depending on whether a conditional transmissionis set, which has characteristics as follows.

-   -   A conditional transmission operation is applied on the basis of        a serving cell in which uplink transmission is performed and the        type of a transmission resource. For example, a conditional        transmission operation is applied only to SPS uplink        transmission of a serving cell configured via RRC, and an        unconditional transmission operation is applied to the remaining        uplink transmission.    -   The conditional transmission operation is applied only when is        it configured via RRC.    -   The conditional transmission operation performs transmission        only when data available for transmission exists even when        uplink grant for initial transmission is available. Otherwise,        transmission is not performed.    -   The data available for transmission includes data available for        transmission in a PDCP layer (defined in the standard 36.323)        and data available for transmission in an RLC layer (defined in        the standard 36.322) and MAC CE (defined in 36.321). The MAC CE        includes uplink MAC CEs remaining after excluding a short BSR, a        truncated BSR, or a long BSR, which is triggered as a padding        BSR. Particularly, a power headroom report, a C-RNTI MAC CE, a        short BSR or long BSR, triggered as a regular BSR, may be        included.    -   If an initial transmission and a non-adaptive retransmission        collide at a TTI for a UE configured with a conditional        transmission operation, transmission is performed by selecting        one of the initial transmission and the non-adaptive        retransmission according to the type of transmission resource of        the initial transmission.    -   If non-adaptive retransmission collides with initial        transmission due to an SPS (or a configured uplink grant),        non-adaptive retransmission is performed. Initial transmission        is performed at the closest point in time at which a collision        with non-adaptive retransmission does not occur.    -   If non-adaptive retransmission collides with initial        transmission by normal uplink grant, initial transmission is        performed.

FIG. 4A is a diagram illustrating the overall operation of the presentdisclosure according to an embodiment of the present disclosure.

Referring to FIG. 4A, a mobile communication system includes a UE 4a-05, a base station 4 a-10, and other nodes. In operation 4 a-15, theUE 4 a-05 establishes an RRC connection with a base station. The factthat the UE 4 a-05 and the base station 4 a-10 establish an RRCconnection indicates that a signaling radio bearer (SRB) is configuredbetween the UE 4 a-05 and the base station 4 a-10 such that an RRCcontrol message may be transmitted and received therebetween. The RRCconnection establishment is performed via a random access process, andincludes processes in which the UE 4 a-05 transmits an RRC connectionestablishment request message to the base station 4 a-10, the basestation 4 a-10 transmits an RRC connection establishment message to theUE 4 a-05, and the UE 4 a-05 transmits an RRC connection establishmentcomplete message to the base station 4 a-10.

After establishment of an RRC connection, the base station 4 a-10indicates RRC connection reestablishment to the UE 4 a-05 in operation 4a-20. Via the RRC connection reestablishment message, SPS configurationinformation is transferred to the UE 4 a-05, and whether to apply aconditional transmission operation is indicated. Information indicatingwhether to apply a conditional transmission operation may be included insub-information of sps-ConfigUL of the RRC connection reconfigurationmessage (RRCConnectionReconfiguration), and may be defined in the formof ENUMERATED {SETUP}, being named SkipUplinkTransmission. For example,if SkipUplinkTransmission, indicating SETUP, is included in sps-ConfigULof an RRCConnectionReconfiguration message that the UE 4 a-05 receives,the fact indicates a conditional transmission operation forpreconfigured PUSCH transmission of a preconfigured serving cell.Otherwise, an unconditional transmission operation for all PUSCHtransmission is indicated. The preconfigured serving cell is indicatedusing information named SemiPersistSchedSCell.

If new data is generated in operation 4 a-25, the UE 4 a-05 may waituntil a new transmission resource for new data transmission becomesavailable.

If an uplink transmission resource for new uplink transmission isavailable in operation 4 a-27 (UL resource allocated for newtransmission is available), the UE 4 a-05 proceeds with operation 4 a-30and determines whether to perform uplink transmission. The uplinktransmission resource available for the new transmission may be atransmission resource allocated via a PDCCH addressed by a C-RNTI of theUE 4 a-05, or may be a transmission resource for SPS, that is, aconfigured uplink grant (configured UL grant).

In operation 4 a-30, the UE 4 a-05 determines whether to performtransmission via the uplink transmission resource (or whether togenerate a MAC PDU to be transmitted via the uplink transmissionresource) by taking into consideration the existence of SPS-ConfigUL,SkipUplinkTransmission, and SemiPersistSchedSCell, and the valuesthereof, the characteristic of an available transmission resource, andthe existence of data available for transmission, and may or may notperform uplink transmission. More particularly, the UE 4 a-05 maydetermine whether to perform uplink transmission as below.

-   -   If the transmission resource is an SPS resource,        SkipUplinkTransmission is configured, and data to be transmitted        via the transmission resource for the uplink transmission does        not exist, the UE 4 a-05 may not perform new uplink        transmission.    -   If the transmission resource is an SPS resource,        SkipUplinkTransmission is configured, data to be transmitted via        the transmission resource for the uplink transmission exists,        and the new uplink transmission does not overlap (or collide)        with another transmission, e.g., HARQ retransmission, the UE 4        a-05 may perform new uplink transmission using the transmission        resource.    -   If the new uplink transmission overlaps with HARQ        retransmission, the UE 4 a-05 may not perform new uplink        transmission but may perform HARQ retransmission. The UE        determines a subframe and a HARQ process to be used for        transmitting new data as below.    -   A HARQ process and the subframe that is the closest to a        corresponding point in time may be selected from among subframes        in which an SPS transmission resource for new transmission is        allocated and a buffer of a related HARQ process is empty, and        new transmission is performed. If a transmission resource        allocated via a PDCCH addressed by C-RNTI of the UE 4 a-05 is        available at a point in time earlier than the determined point        in time, new transmission is performed using the dynamically        allocated transmission resource.

Otherwise, the UE 4 a-05 performs new transmission using the determinedHARQ process at the determined point in time in operation 4 a-35.

HARQ new transmission is preferentially performed over HARQretransmission when the conditional transmission is configured, as shownin operations 4 a-30 and 4 a-35, since the base station 4 a-10 hasdifficulty determining whether the transmission by the UE 4 a-05 is HARQretransmission or HARQ new transmission when the conditionaltransmission is configured. Therefore, if the UE 4 a-05 performs HARQnew transmission in a subframe in which the base station 4 a-10 expectsHARQ retransmission, the base station 4 a-10 may not perform softcombining well, and thus uplink transmission may fail.

FIG. 4B is a diagram illustrating operations of a UE according to anembodiment of the present disclosure.

Referring to FIG. 4B, in operation 4 b-05, a UE receives aRRCConnectionReconfiguration control message from a base station. Thecontrol message may include information indicating whether firsttransmission is configured and SPS transmission resource configurationinformation. The configuration of the first transmission indicatesconfiguration of conditional transmission, and whether the conditionaltransmission is configured may be indicated depending on whetherpreconfigured control information such as SkipUplinkTransmission isincluded.

In operation 4 b-10, the UE may have new data available fortransmission. The UE may determine whether the new data available fortransmission exists.

In operation 4 b-15, the UE may select a subframe and a HARQ process tobe used for transmitting the new data available for transmission.

In operation 4 b-20, the UE determines whether HARQ retransmission isscheduled in the selected subframe. The UE proceeds with operation 4b-25 if HARQ retransmission is scheduled, and proceeds with operation 4b-40 to perform new transmission in the subframe if the new transmissiondoes not overlap with HARQ retransmission. If HARQ retransmission isscheduled, it is determined that a collision with HARQ retransmission isto occur. If HARQ retransmission is not scheduled, it is determined thata collision with the HARQ retransmission is not to occur.

In operation 4 b-25, the UE may determine whether to perform newtransmission or HARQ retransmission in the subframe. The UE maydetermine whether the first transmission is configured.

If a semi-persistent transmission resource isconfigured/allocated/activated, the period of the semi-persistenttransmission resource is a preconfigured value (e.g., 1 ms), and thefirst transmission is configured for the semi-persistent transmission,the UE proceeds with operation 4 b-30, and perform HARQ retransmissionin the subframe. The UE proceeds with operation 4 b-35 in order toselect a subframe in which new transmission is to be performed.

If a semi-persistent transmission resource isconfigured/allocated/activated and the first transmission is notconfigured for semi-persistent transmission, the UE proceeds withoperation 4 b-37, discards data stored in a HARQ process related to thesubframe (i.e. data for which HARQ retransmission is scheduled), andperforms new transmission in the subframe.

In operation 4 b-35, the UE selects a subframe in which a related HARQbuffer is empty (i.e., in which HARQ retransmission is not scheduled)from among subframes in which a semi-persistent transmission resource isallocated and performs new transmission in the subframe. Alternatively,the UE selects one of the HARQ processes having empty HARQ buffers fromamong HARQ processes, and may perform new transmission in a subframerelated to the selected HARQ process.

If the conditional transmission is configured, the base station hasdifficulty determining whether transmission by the UE is HARQretransmission or HARQ new transmission. Accordingly, as another method,a scheme may be considered in which retransmission is performed onlywhen a base station indicates retransmission if the conditionaltransmission is configured.

Uplink HARQ retransmission may include non-adaptive retransmission andadaptive retransmission. Non-adaptive retransmission performsretransmission on the basis of only HARQ feedback information.Non-adaptive retransmission is a scheme that performs retransmission byapplying a transmission resource and a transmission format which wereused in a previous transmission if a HARQ NACK is received. Adaptiveretransmission is a scheme that performs retransmission by applying atransmission resource and a transmission format explicitly indicated bybase station.

If conditional transmission is not configured, both non-adaptiveretransmission and adaptive-retransmission are used. If conditionaltransmission is configured, only adaptive retransmission is used.Accordingly, the above-described drawback is overcome.

FIG. 4C is a diagram illustrating the operation of a UE according to anembodiment of the present disclosure.

Referring to FIG. 4C, in operation 4 c-05, a UE receives anRRCConnectionReconfiguration control message from a base station.Whether first transmission is configured may be indicated via thecontrol message. The configuration of the first transmission indicatesconfiguration of conditional transmission, and whether the conditionaltransmission is configured may be indicated depending on whetherpreconfigured control information such as SkipUplinkTransmission isincluded.

In operation 4 c-10, the UE performs uplink transmission.

In operation 4 c-15, the UE waits for a preconfigured period of timeafter performing the uplink transmission, and sets a parameter relatedto HARQ feedback. In this instance, if the uplink transmissioncorresponds to second transmission, the UE receives HARQ feedbackinformation indicated by the base station a preconfigured period of timeafter performing the uplink transmission and sets the HARQ feedbackparameter to the received value. If the uplink transmission correspondsto the first transmission, the UE may not receive HARQ feedbackinformation and may set the HARQ feedback parameter to HARQ ACK, or eventhough the UE receives the HARQ feedback information, the UE may set theHARQ feedback parameter to HARQ ACK without taking into considerationthe received HARQ feedback.

The HARQ feedback parameter is a parameter for controlling HARQretransmission. The fact that the HARQ feedback parameter is set to ACKmay indicate that retransmission is performed only when retransmissionis explicitly indicated via a PDCCH. The fact that the HARQ feedbackparameter is set to NACK may indicate that non-adaptive HARQretransmission is performed even when retransmission is not explicitlyindicated via a PDCCH.

In operation 4 c-20, the UE determines whether to perform retransmissionby taking into consideration the type of transmission, a HARQ feedbackparameter, and whether an explicit retransmission command is received,so as to perform retransmission.

In the case of the second transmission, the UE may perform firstretransmission or second retransmission, or may not performretransmission on the basis of whether a PDCCH is received and a HARQfeedback parameter. If a PDCCH indicating retransmission is not receivedand a HARQ feedback is NACK, the second retransmission is performed. Ifa PDCCH indicating retransmission is received, the first retransmissionis performed. If a PDCCH indicating retransmission is not received andHARQ feedback is ACK, retransmission is not performed.

In the case of the first transmission, the UE may perform the firstretransmission or may not perform retransmission on the basis of whethera PDCCH is received. If a PDCCH indicating retransmission is received,the first retransmission is performed. If a PDCCH indicatingretransmission is not received, retransmission is not performed.

The first retransmission indicates retransmission performed using atransmission resource and a transmission format explicitly indicated bya PDCCH, instead of using a transmission resource and a transmissionformat used in the previous transmission. The transmission formatindicates, for example, the size of a transport block, a modulationscheme, a coding rate, and the like.

The second retransmission indicates retransmission performed using atransmission resource and a transmission format which were used in theprevious transmission.

In the embodiment of the present disclosure, the second transmissionindicates unconditional transmission performed when a transmissionresource is available although data to be transmitted does not exist.Also, in the embodiment of the present disclosure, the firsttransmission indicates conditional transmission performed only when datathat is to be transmitted and satisfies a preconfigured condition existsalthough a transmission resource is available.

FIG. 4D is a diagram of the structure of a UE according to an embodimentof the present disclosure.

Referring to FIG. 4D, the UE may include a radio-frequency (RF)processor 4 d-10, a baseband processor 4 d-20, a storage unit 4 d-30,and a controller 4 d-40.

The RF processor 4 d-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 4 d-10 up-convertsa baseband signal provided from the baseband processor 4 d-20 into an RFband signal, transmits the RF band signal via an antenna, anddown-converts the RF band signal received via the antenna into abaseband signal. For example, the RF processor 4 d-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. Although only one antenna is illustratedin FIG. 4, the UE may include a plurality of antennas. In addition, theRF processor 4 d-10 may include a plurality of RF chains. Moreover, theRF processor 4 d-10 may perform beamforming. For the beamforming, the RFprocessor 4 d-10 may control the phase and the size of each signaltransmitted/received via a plurality of antennas or antenna elements.Also, the RF processor may perform MIMO operation, and may receive aplurality of layers while performing MIMO operation.

The baseband processor 4 d-20 performs a function for conversion betweena baseband signal and a bitstream according to the physical layerstandard of the system. For example, in the case of data transmission,the baseband processor 4 d-20 generates complex symbols by encoding andmodulating a transmission bitstream. Further, in the case of datareception, the baseband processor 4 d-20 reconstructs a receptionbitstream by demodulating and decoding a baseband signal provided fromthe RF processor 4 d-10. For example, according to anorthogonal-frequency-division-multiplexing (OFDM) scheme, in the case ofdata transmission, the baseband processor 4 d-20 generates complexsymbols by encoding and modulating a transmission bitstream, maps thecomplex symbols to subcarriers, and then configures OFDM symbols via anIFFT (inverse fast Fourier transform) operation and a cyclic prefix (CP)insertion. Further, in the case of data reception, the basebandprocessor 4 d-20 divides the baseband signal provided from the RFprocessor 4 d-10 into OFDM symbol units, reconstructs the signals mappedto the subcarriers via a fast Fourier transform (FFT) operation, andthen reconstructs a reception bitstream via demodulation and decoding.

The baseband processor 4 d-20 and the RF processor 4 d-10 transmit andreceive a signal, as described above. Accordingly, each of the basebandprocessor 4 d-20 and the RF processor 4 d-10 may be referred to as atransmitter, a receiver, a transceiver, or a communication unit. Inaddition, at least one of the baseband processor 4 d-20 or the RFprocessor 4 d-10 may include a plurality of communication modules so asto support many different radio access technologies. In addition, atleast one of the baseband processor 4 d-20 or the RF processor 4 d-10may include different communication modules to process signals ofdifferent frequency bands. For example, the different communicationstandards may include a wireless LAN (e.g., IEEE 802.11) and a cellularnetwork (e.g., LTE). Further, the different frequency bands may includea super-high frequency (SHF) (e.g., 2.5 GHz and 5 GHz) band and amillimeter (mm) wave (e.g., 60 GHz) band.

The storage unit 4 d-30 stores data such as a basic program, anapplication program, and configuration information for the operation ofthe UE. The storage unit 4 d-30 may provide stored data in response to arequest from the controller 4 d-40.

The controller 4 d-40 may control the overall operation of the UE. Forexample, the controller 4 d-40 transmits and receives a signal via thebaseband processor 4 d-20 and the RF processor 4 d-10. Also, thecontroller 4 d-40 writes and reads data to/from the storage unit 4 d-40.To this end, the controller 4 d-40 may include at least one processor.For example, the controller 4 d-40 may include a communication processor(CP), which performs control for communication, and an applicationprocessor (AP), which controls a higher layer such as an applicationprogram. The controller 2 g-40 may include a multiple-access processor 2g-42. According to an embodiment of the present disclosure, thecontroller 4 d-40 may perform control such that the UE performs theoperations and procedures described in FIGS. 4A, 4B, and 4C.

FIG. 4E is a block diagram of a main base station in a wirelesscommunication system according to an embodiment of the presentdisclosure.

Referring to FIG. 4E, the base station may include an RF processor 4e-10, a baseband processor 4 e-20, a backhaul communication unit 4 e-30,a storage unit 4 e-40, and a controller 4 e-50.

The RF processor 4 e-10 performs a function of transmitting andreceiving a signal via a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 4 e-10 up-convertsa baseband signal provided from the baseband processor 4 e-20 into an RFband signal and then transmits the converted signal via an antenna, anddown-converts an RF band signal received via the antenna into a basebandsignal. For example, the RF processor 4 e-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although only a single antenna is illustrated in FIG. 15, afirst access node may include a plurality of antennas. In addition, theRF processor 4 e-10 may include a plurality of RF chains. Moreover, theRF processor 4 e-10 may perform beamforming. For the beamforming, the RFprocessor 4 e-10 may control the phase and the size of each of thesignals transmitted and received via a plurality of antennas or antennaelements. The RF processor may perform downlink MIMO operation bytransmitting one or more layers.

The baseband processor 4 e-20 performs a function of converting betweena baseband signal and a bitstream according to the physical layerstandard of a first radio access technology. For example, in the case ofdata transmission, the baseband processor 4 e-20 generates complexsymbols by encoding and modulating a transmission bitstream. Further, inthe case of data reception, the baseband processor 4 e-20 reconstructs areception bitstream by demodulating and decoding a baseband signalprovided from the RF processor 4 e-10. For example, according to an OFDMscheme, in the case of data transmission, the baseband processor 4 e-20generates complex symbols by encoding and modulating the transmissionbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols via an IFFT operation and CP insertion. Also, in the caseof data reception, the baseband processor 4 e-20 divides a basebandsignal provided from the RF processor 4 e-10 into OFDM symbol units,restores signals mapped onto the subcarriers via the FFT operation, andrestores a reception bitstream via demodulation and decoding. Thebaseband processor 4 e-20 and the RF processor 4 e-10 transmit andreceive a signal as described above. Accordingly, each of the basebandprocessor 4 e-20 and the RF processor 4 e-10 may be referred to as atransmitter, a receiver, a transceiver, a communication unit, or awireless communication unit.

The backhaul communication unit 4 e-30 provides an interface forperforming communication with other nodes in a network. That is, thebackhaul communication unit 4 e-30 may convert, into a physical signal,a bitstream transmitted from the main base station to another node, forexample, a secondary base station, a core network, and the like, and mayconvert a physical signal received from another node into a bitstream.

The storage unit 4 e-40 may store data, such as a basic program, anapplication program, configuration information, or the like, used foroperating the main base station. Particularly, the storage unit 4 e-40may store information associated with a bearer allocated to a connectedUE, a measurement result reported from a connected UE, and the like.Also, the storage unit 4 e-40 may store information which is a criterionto determine whether to provide or interrupt multiple access to a UE.The storage unit 4 e-40 may provide stored data in response to a requestfrom the controller 4 e-50.

The controller 4 e-50 may control the overall operation of the main basestation. For example, the controller 4 e-50 may transmit and receive asignal via the baseband processor 4 e-20 and the RF processor 4 e-10 orthe backhaul communication unit 4 e-30. Also, the controller 4 e-50writes and reads data to/from the storage unit 4 e-40. To this end, thecontroller 4 e-50 may include at least one processor. According to anembodiment of the present disclosure, the controller 4 e-50 may includea multiple-access controller 4 e-52 that performs control so as toprovide multiple access to the UE. For example, the controller 4 e-50may perform control such that the main base station performs operationsand procedures of the node B illustrated in FIG. 4A. Also, thecontroller 4 e-50 may perform control such that the main node B performsoperations and procedures of a node B corresponding to the operations ofthe UE described in FIGS. 4B and 4C.

In the above-described detailed embodiments of the present disclosure, acomponent included in the present disclosure is expressed in thesingular or the plural according to a presented detailed embodiment.However, the singular form or plural form is selected for convenience ofdescription suitable for the presented situation, and variousembodiments of the present disclosure are not limited to a singleelement or multiple elements thereof. Further, either multiple elementsexpressed in the description may be configured into a single element ora single element in the description may be configured into multipleelements.

Meanwhile, while the disclosure has been shown and described withreference to specific embodiments thereof in the detailed description ofthe present disclosure, it goes without saying that various changes inform and details may be made therein without departing from the spiritand scope of the disclosure. Therefore, the scope of the presentdisclosure should not be defined as being limited to the embodiments,but should be defined by the appended claims and equivalents thereof.

The invention claimed is:
 1. A method of selecting a beam by a userequipment (UE), the method comprising: receiving system informationincluding first beam reselection priority information; receiving a radioresource control (RRC) message including second beam reselectionpriority information; identifying whether the UE camps on a suitablebeam based on a beamforming capability of the UE; and applying one ofthe first beam reselection priority information and the second beamreselection priority information based on a result of theidentification, wherein the beamforming capability of the UE comprisesat least one of a number of beams, a beam width, a gain of a beam, amaximum gain of a beam, an antenna pattern, an orientation of a beam, aresolution of beamforming, a maximum transmission power, or a beamsweeping length.
 2. The method as claimed in claim 1, wherein thebeamforming capability of the UE corresponds to at least one beamformingfactor, and the beamforming capability is defined for each frequencyband.
 3. The method as claimed in claim 1, wherein if the UE does notcamp on a suitable beam, the first beam reselection priority informationis applied.
 4. The method as claimed in claim 1, wherein if the UE campson a suitable beam, the second beam reselection priority information isapplied.
 5. The method as claimed in claim 1, wherein, if the UE campson a suitable beam and satisfies a preconfigured condition, the secondbeam reselection priority information is deleted.
 6. A user equipment(UE), comprising: a transceiver configured to transmit and receive asignal; and a controller coupled with the transceiver and configured to:receive system information including first beam reselection priorityinformation, receive a radio resource control (RRC) message includingsecond beam reselection priority information, identify whether the UEcamps on a suitable beam based on a beamforming capability of the UE,and apply one of the first beam reselection priority information and thesecond beam reselection priority information based on a result of theidentification, wherein the beamforming capability of the UE comprisesat least one of a number of beams, a beam width, a gain of a beam, amaximum gain of a beam, an antenna pattern, an orientation of a beam, aresolution of beamforming, a maximum transmission power, or a beamsweeping length.
 7. The UE as claimed in claim 6, wherein thebeamforming capability of the UE corresponds to at least one beamformingfactor, and the beamforming capability is defined for each frequencyband.
 8. The UE as claimed in claim 6, wherein, if the UE does not campon a suitable beam, the first beam reselection priority information isapplied.
 9. The UE as claimed in claim 6, wherein, if the UE camps on asuitable beam, the second beam reselection priority information isapplied.
 10. The UE as claimed in claim 6, wherein, if the UE camps on asuitable beam and satisfies a preconfigured condition, the second beamreselection priority information is deleted.